diff --git a/Cargo.lock b/Cargo.lock
index 8f48fcd..d5f1a70 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1074,6 +1074,12 @@ version = "6.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "21326818e99cfe6ce1e524c2a805c189a99b5ae555a35d19f9a284b427d86afa"
 
+[[package]]
+name = "parse-size"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "944553dd59c802559559161f9816429058b869003836120e262e8caec061b7ae"
+
 [[package]]
 name = "peeking_take_while"
 version = "0.1.2"
@@ -1166,6 +1172,7 @@ dependencies = [
  "lazy_static",
  "link-cplusplus",
  "modular-bitfield",
+ "parse-size",
  "proc_macros",
  "regex",
  "reqwest",
diff --git a/Cargo.toml b/Cargo.toml
index 1487f71..c70ad92 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -23,6 +23,7 @@ int-enum = "0.4"
 json = "0.12"
 lazy_static = "1.4"
 modular-bitfield = "0.11"
+parse-size = "1"
 proc_macros = { path = "proc_macros" }
 regex = "1"
 reqwest = { version = "0.11", features = ["brotli", "deflate", "gzip", "rustls-tls", "socks", "stream"] }
diff --git a/src/downloader/downloader.rs b/src/downloader/downloader.rs
index b8e9668..8c02aab 100644
--- a/src/downloader/downloader.rs
+++ b/src/downloader/downloader.rs
@@ -33,6 +33,7 @@ use std::ops::DerefMut;
 use std::path::Path;
 use std::sync::atomic::AtomicBool;
 use std::sync::atomic::AtomicI64;
+use std::sync::atomic::AtomicU32;
 use std::sync::atomic::AtomicU64;
 use std::sync::Arc;
 use std::sync::RwLock;
@@ -86,6 +87,8 @@ pub struct DownloaderInternal<T: Write + Seek + Send + Sync + ClearFile + GetTar
     pub max_part_retry_count: AtomicI64,
     /// The maximun threads to download file.
     pub max_threads: AtomicU64,
+    /// The size of the each part when downloading file.
+    part_size: AtomicU32,
 }
 
 impl DownloaderInternal<LocalFile> {
@@ -167,6 +170,7 @@ impl DownloaderInternal<LocalFile> {
             retry_count: AtomicI64::new(0),
             max_part_retry_count: AtomicI64::new(3),
             max_threads: AtomicU64::new(8),
+            part_size: AtomicU32::new(0x10000),
         }))
     }
 }
@@ -255,6 +259,16 @@ impl<T: Write + Seek + Send + Sync + ClearFile + GetTargetFileName> DownloaderIn
         self.error.get_mut().take()
     }
 
+    #[inline]
+    /// Return the size of the each part
+    pub fn get_part_size(&self) -> u32 {
+        if self.pd.is_downloading() {
+            self.pd.get_part_size()
+        } else {
+            self.part_size.qload()
+        }
+    }
+
     /// Increase the retry count and return the duration should waited.
     /// If [None] is returned, should stop retry.
     pub fn get_retry_duration(&self) -> Option<Duration> {
@@ -356,6 +370,12 @@ impl<T: Write + Seek + Send + Sync + ClearFile + GetTargetFileName> DownloaderIn
         self.error.get_mut().replace(err);
     }
 
+    #[inline]
+    /// Set the size of the each part when downloading file
+    pub fn set_part_size(&self, part_size: u32) {
+        self.part_size.qsave(part_size)
+    }
+
     #[inline]
     /// Sets the length of the progress bar
     pub fn set_progress_bar_length(&self, length: u64) {
@@ -483,6 +503,18 @@ impl<T: Write + Seek + Send + Sync + ClearFile + GetTargetFileName + 'static> Do
         if !self.is_created() {
             return self.downloader.get_status();
         }
+        if !self.downloader.is_downloading() && self.is_multi_threads() {
+            match self
+                .downloader
+                .pd
+                .set_part_size(self.downloader.get_part_size())
+            {
+                Ok(_) => {}
+                Err(e) => {
+                    println!("{}", e);
+                }
+            }
+        }
         self.downloader.set_downloading();
         tokio::spawn(check_tasks(Arc::clone(&self.downloader)));
         self.downloader.get_status()
@@ -556,6 +588,7 @@ impl<T: Write + Seek + Send + Sync + ClearFile + GetTargetFileName + 'static> Do
             self.enable_multiple_download()
         }
         self.set_max_threads(helper.max_threads());
+        self.set_part_size(helper.part_size());
     }
 
     #[inline]
@@ -578,6 +611,12 @@ impl<T: Write + Seek + Send + Sync + ClearFile + GetTargetFileName + 'static> Do
         self.downloader.set_max_threads(max_threads)
     }
 
+    #[inline]
+    /// Set the size of the each part when downloading file
+    pub fn set_part_size(&self, part_size: u32) {
+        self.downloader.set_part_size(part_size)
+    }
+
     #[inline]
     /// Set the retry interval.
     pub fn set_retry_interval(&self, retry_interval: NonTailList<Duration>) {
diff --git a/src/downloader/pd_file/file.rs b/src/downloader/pd_file/file.rs
index 01dcdb2..728ef68 100644
--- a/src/downloader/pd_file/file.rs
+++ b/src/downloader/pd_file/file.rs
@@ -46,6 +46,8 @@ const TYPE_OFFSET: SeekFrom = SeekFrom::Start(11);
 const FILE_SIZE_OFFSET: SeekFrom = SeekFrom::Start(12);
 /// The offset of the downloaded_file_size in pd file
 const DOWNLOADED_FILE_SIZE_OFFSET: SeekFrom = SeekFrom::Start(20);
+/// The offset of the part_size in pd file
+const PART_SIZE_OFFSET: SeekFrom = SeekFrom::Start(28);
 
 #[derive(Debug)]
 /// The pd file
@@ -185,6 +187,12 @@ impl PdFile {
         }
     }
 
+    #[inline]
+    /// Return the size of the each part.
+    pub fn get_part_size(&self) -> u32 {
+        self.part_size.qload()
+    }
+
     /// Increase the downloaded file size.
     /// * `size` - The file size want to added.
     ///
@@ -441,6 +449,20 @@ impl PdFile {
         Ok(())
     }
 
+    /// Set the size of the each part. Ignored in single thread mode.
+    pub fn set_part_size(&self, part_size: u32) -> Result<(), PdFileError> {
+        self.part_size.qstore(part_size);
+        if !self.is_mem_only() {
+            self.need_saved.qstore(true);
+            let mut f = self.file.get_mut();
+            let f = f.as_mut().unwrap();
+            f.seek(PART_SIZE_OFFSET)?;
+            f.write_le_u32(part_size)?;
+            self.need_saved.qstore(false);
+        }
+        Ok(())
+    }
+
     /// Write all data to the file.
     pub fn write(&self) -> Result<(), PdFileError> {
         let mut f = self.file.get_mut();
diff --git a/src/main.rs b/src/main.rs
index a5ec5b7..7590843 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -17,6 +17,7 @@ extern crate lazy_static;
 #[cfg(all(feature = "link-cplusplus", target_env = "gnu"))]
 extern crate link_cplusplus;
 extern crate modular_bitfield;
+extern crate parse_size;
 extern crate proc_macros;
 extern crate regex;
 extern crate reqwest;
diff --git a/src/opt/mod.rs b/src/opt/mod.rs
index 12b4b24..d23532c 100644
--- a/src/opt/mod.rs
+++ b/src/opt/mod.rs
@@ -1 +1,2 @@
+pub mod size;
 pub mod use_progress_bar;
diff --git a/src/opt/size.rs b/src/opt/size.rs
new file mode 100644
index 0000000..b0dfee7
--- /dev/null
+++ b/src/opt/size.rs
@@ -0,0 +1,27 @@
+use json::JsonValue;
+use std::convert::TryFrom;
+
+/// Parse file size
+pub fn parse_size(obj: &JsonValue) -> Option<u64> {
+    match obj.as_u64() {
+        Some(s) => Some(s),
+        None => match obj.as_str() {
+            Some(s) => match parse_size::parse_size(s) {
+                Ok(s) => Some(s),
+                Err(_) => None,
+            },
+            None => None,
+        },
+    }
+}
+
+/// Parse file size as [i32]
+pub fn parse_u32_size(obj: &JsonValue) -> Option<u32> {
+    match parse_size(obj) {
+        Some(s) => match u32::try_from(s) {
+            Ok(s) => Some(s),
+            Err(_) => None,
+        },
+        None => None,
+    }
+}
diff --git a/src/opthelper.rs b/src/opthelper.rs
index 5d1f02c..d3e677a 100644
--- a/src/opthelper.rs
+++ b/src/opthelper.rs
@@ -5,6 +5,7 @@ use crate::ext::rw_lock::GetRwLock;
 use crate::ext::use_or_not::ToBool;
 use crate::ext::use_or_not::UseOrNot;
 use crate::list::NonTailList;
+use crate::opt::size::parse_u32_size;
 use crate::opt::use_progress_bar::UseProgressBar;
 use crate::opts::CommandOpts;
 use crate::retry_interval::parse_retry_interval_from_json;
@@ -139,6 +140,21 @@ impl OptHelper {
         false
     }
 
+    /// Return the size of the each part when downloading file.
+    pub fn part_size(&self) -> u32 {
+        match self.opt.get_ref().part_size {
+            Some(r) => {
+                return r;
+            }
+            None => {}
+        }
+        let re = self.settings.get_ref().get("part-size");
+        if re.is_some() {
+            return parse_u32_size(re.as_ref().unwrap()).unwrap();
+        }
+        65536
+    }
+
     pub fn update(&self, opt: CommandOpts, settings: SettingStore) {
         if settings.have("author-name-filters") {
             self._author_name_filters.replace_with2(
diff --git a/src/opts.rs b/src/opts.rs
index 38fa18b..0018fc0 100644
--- a/src/opts.rs
+++ b/src/opts.rs
@@ -9,8 +9,10 @@ use crate::utils::check_file_exists;
 use crate::utils::get_exe_path_else_current;
 use getopts::HasArg;
 use getopts::Options;
+use std::convert::TryFrom;
 use std::env;
 use std::num::ParseIntError;
+use std::num::TryFromIntError;
 use std::str::FromStr;
 use std::time::Duration;
 
@@ -82,6 +84,8 @@ pub struct CommandOpts {
     pub download_part_retry: Option<i64>,
     /// The maximun threads when downloading file.
     pub max_threads: Option<u64>,
+    /// The size of the each part when downloading file.
+    pub part_size: Option<u32>,
 }
 
 impl CommandOpts {
@@ -107,6 +111,7 @@ impl CommandOpts {
             multiple_threads_download: None,
             download_part_retry: None,
             max_threads: None,
+            part_size: None,
         }
     }
 
@@ -152,6 +157,15 @@ pub fn print_usage(prog: &str, opts: &Options) {
     println!("{}", opts.usage(brief.as_str()));
 }
 
+/// Error when parsing size
+#[derive(Debug, derive_more::Display, derive_more::From)]
+pub enum ParseSizeError {
+    /// Failed to parse size.
+    ParseSize(parse_size::Error),
+    /// The size is too big.
+    Overflow(TryFromIntError),
+}
+
 /// Prase [bool] from string
 pub fn parse_bool<T: AsRef<str>>(s: Option<T>) -> Result<Option<bool>, String> {
     let tmp = match s {
@@ -189,6 +203,17 @@ pub fn parse_i64<T: AsRef<str>>(s: Option<T>) -> Result<Option<i64>, ParseIntErr
     }
 }
 
+/// Prase size as [u32] from string
+pub fn parse_u32_size<T: AsRef<str>>(s: Option<T>) -> Result<Option<u32>, ParseSizeError> {
+    match s {
+        Some(s) => {
+            let s = parse_size::parse_size(s.as_ref())?;
+            Ok(Some(u32::try_from(s)?))
+        }
+        None => Ok(None),
+    }
+}
+
 /// Prase [u64] from string
 pub fn parse_u64<T: AsRef<str>>(s: Option<T>) -> Result<Option<u64>, ParseIntError> {
     match s {
@@ -328,6 +353,12 @@ pub fn parse_cmd() -> Option<CommandOpts> {
         gettext("The maximun threads when downloading file."),
         "COUNT",
     );
+    opts.optopt(
+        "k",
+        "part-size",
+        gettext("The size of the each part when downloading file."),
+        "SIZE",
+    );
     let result = match opts.parse(&argv[1..]) {
         Ok(m) => m,
         Err(err) => {
@@ -526,6 +557,15 @@ pub fn parse_cmd() -> Option<CommandOpts> {
             return None;
         }
     }
+    match parse_u32_size(result.opt_str("part-size")) {
+        Ok(r) => {
+            re.as_mut().unwrap().part_size = r;
+        }
+        Err(e) => {
+            println!("{} {}", gettext("Failed to parse part size:"), e);
+            return None;
+        }
+    }
     re
 }
 
diff --git a/src/settings_list.rs b/src/settings_list.rs
index da4d926..fe924bd 100644
--- a/src/settings_list.rs
+++ b/src/settings_list.rs
@@ -5,6 +5,7 @@ use crate::gettext;
 use crate::retry_interval::check_retry_interval;
 use crate::settings::SettingDes;
 use crate::settings::JsonValueType;
+use crate::opt::size::parse_u32_size;
 use json::JsonValue;
 
 pub fn get_settings_list() -> Vec<SettingDes> {
@@ -26,6 +27,7 @@ pub fn get_settings_list() -> Vec<SettingDes> {
         SettingDes::new("multiple-threads-download", gettext("Whether to enable multiple threads download."), JsonValueType::Boolean, None).unwrap(),
         SettingDes::new("download-part-retry", gettext("Max retry count of each part when downloading in multiple thread mode."), JsonValueType::Number, Some(check_i64)).unwrap(),
         SettingDes::new("max-threads", gettext("The maximun threads when downloading file."), JsonValueType::Number, Some(check_u64)).unwrap(),
+        SettingDes::new("part-size", gettext("The size of the each part when downloading file."), JsonValueType::Number, Some(check_parse_size_u32)).unwrap(),
     ]
 }
 
@@ -39,6 +41,11 @@ fn check_u64(obj: &JsonValue) -> bool {
     r.is_some()
 }
 
+#[inline]
+fn check_parse_size_u32(obj: &JsonValue) -> bool {
+    parse_u32_size(obj).is_some()
+}
+
 fn check_nonempty_str(obj: &JsonValue) -> bool {
     let r = obj.as_str();
     r.is_some() && r.unwrap().len() != 0