diff --git a/ch3/os/src/syscall/mod.rs b/ch3/os/src/syscall/mod.rs
index 0f9f63c..4b907ee 100644
--- a/ch3/os/src/syscall/mod.rs
+++ b/ch3/os/src/syscall/mod.rs
@@ -1,5 +1,6 @@
 const SYSCALL_WRITE: usize = 64;
 const SYSCALL_EXIT: usize = 93;
+const SYSCALL_YIELD: usize = 124;
 
 mod fs;
 mod process;
@@ -12,6 +13,7 @@ pub fn syscall(syscall_id: usize, args: [usize; 3]) -> isize {
     match syscall_id {
         SYSCALL_WRITE => sys_write(args[0], args[1] as *const u8, args[2]),
         SYSCALL_EXIT => sys_exit(args[0] as i32),
+        SYSCALL_YIELD => sys_yield(),
         _ => panic!("Unsupported syscall_id: {}", syscall_id),
     }
 }
\ No newline at end of file
diff --git a/ch3/os/src/syscall/process.rs b/ch3/os/src/syscall/process.rs
index 331d9b5..03fef54 100644
--- a/ch3/os/src/syscall/process.rs
+++ b/ch3/os/src/syscall/process.rs
@@ -1,7 +1,7 @@
 //! App management syscalls
 // use crate::batch::run_next_app;
 use crate::println;
-use crate::task::exit_current_and_run_next;
+use crate::task::{exit_current_and_run_next, suspend_current_and_run_next};
 
 /// 任务退出, 并立即切换任务
 pub fn sys_exit(exit_code: i32) -> ! {
@@ -9,3 +9,8 @@ pub fn sys_exit(exit_code: i32) -> ! {
     exit_current_and_run_next();
     panic!("Unreachable in sys_exit!");
 }
+
+pub fn sys_yield() -> isize {
+    suspend_current_and_run_next();
+    0
+}
\ No newline at end of file
diff --git a/ch3/user/src/bin/00write_a.rs b/ch3/user/src/bin/00write_a.rs
index 67088ed..3303899 100644
--- a/ch3/user/src/bin/00write_a.rs
+++ b/ch3/user/src/bin/00write_a.rs
@@ -13,7 +13,7 @@ fn main() -> i32 {
             print!("A");
         }
         println!(" [{}/{}]", i + 1, HEIGHT);
-        // sys_yield();
+        sys_yield();
     }
     println!("Test write_a OK!");
     0
diff --git a/ch3/user/src/bin/01write_b.rs b/ch3/user/src/bin/01write_b.rs
index 1ae798f..64bd665 100644
--- a/ch3/user/src/bin/01write_b.rs
+++ b/ch3/user/src/bin/01write_b.rs
@@ -13,7 +13,7 @@ fn main() -> i32 {
             print!("B");
         }
         println!(" [{}/{}]", i + 1, HEIGHT);
-        // sys_yield();
+        sys_yield();
     }
     println!("Test write_b OK!");
     0
diff --git a/ch3/user/src/bin/02write_c.rs b/ch3/user/src/bin/02write_c.rs
index f9c8f71..25464bf 100644
--- a/ch3/user/src/bin/02write_c.rs
+++ b/ch3/user/src/bin/02write_c.rs
@@ -13,7 +13,7 @@ fn main() -> i32 {
             print!("C");
         }
         println!(" [{}/{}]", i + 1, HEIGHT);
-        // sys_yield();
+        sys_yield();
     }
     println!("Test write_c OK!");
     0