diff --git a/os/src/task/manager.rs b/os/src/task/manager.rs
index 5ed68ae7..bdeda5d2 100644
--- a/os/src/task/manager.rs
+++ b/os/src/task/manager.rs
@@ -21,6 +21,14 @@ impl TaskManager {
     pub fn fetch(&mut self) -> Option<Arc<TaskControlBlock>> {
         self.ready_queue.pop_front()
     }
+    pub fn remove(&mut self, task: Arc<TaskControlBlock>) {
+        if let Some((id, _)) = self.ready_queue
+            .iter()
+            .enumerate()
+            .find(|(_, t)| Arc::as_ptr(t) == Arc::as_ptr(&task)) {
+                self.ready_queue.remove(id);
+            }
+    }
 }
 
 lazy_static! {
@@ -34,6 +42,10 @@ pub fn add_task(task: Arc<TaskControlBlock>) {
     TASK_MANAGER.exclusive_access().add(task);
 }
 
+pub fn remove_task(task: Arc<TaskControlBlock>) {
+    TASK_MANAGER.exclusive_access().remove(task);
+}
+
 pub fn fetch_task() -> Option<Arc<TaskControlBlock>> {
     TASK_MANAGER.exclusive_access().fetch()
 }
diff --git a/os/src/task/mod.rs b/os/src/task/mod.rs
index 995a3374..b66490b8 100644
--- a/os/src/task/mod.rs
+++ b/os/src/task/mod.rs
@@ -15,10 +15,11 @@ use lazy_static::*;
 use manager::fetch_task;
 use process::ProcessControlBlock;
 use switch::__switch;
+use crate::timer::remove_timer;
 
 pub use context::TaskContext;
 pub use id::{kstack_alloc, pid_alloc, KernelStack, PidHandle};
-pub use manager::{add_task, pid2process, remove_from_pid2process};
+pub use manager::{add_task, remove_task, pid2process, remove_from_pid2process};
 pub use processor::{
     current_kstack_top, current_process, current_task, current_trap_cx, current_trap_cx_user_va,
     current_user_token, run_tasks, schedule, take_current_task,
@@ -90,6 +91,9 @@ pub fn exit_current_and_run_next(exit_code: i32) {
         let mut recycle_res = Vec::<TaskUserRes>::new();
         for task in process_inner.tasks.iter().filter(|t| t.is_some()) {
             let task = task.as_ref().unwrap();
+            // if other tasks are Ready in TaskManager or waiting for a timer to be
+            // expired, we should remove them.
+            remove_inactive_task(Arc::clone(&task));
             let mut task_inner = task.inner_exclusive_access();
             if let Some(res) = task_inner.res.take() {
                 recycle_res.push(res);
@@ -107,6 +111,8 @@ pub fn exit_current_and_run_next(exit_code: i32) {
         process_inner.memory_set.recycle_data_pages();
         // drop file descriptors
         process_inner.fd_table.clear();
+        // remove all tasks
+        process_inner.tasks.clear();
     }
     drop(process);
     // we do not have to save task context
@@ -137,3 +143,8 @@ pub fn current_add_signal(signal: SignalFlags) {
     let mut process_inner = process.inner_exclusive_access();
     process_inner.signals |= signal;
 }
+
+pub fn remove_inactive_task(task: Arc<TaskControlBlock>) {
+    remove_task(Arc::clone(&task));
+    remove_timer(Arc::clone(&task));
+}
diff --git a/os/src/timer.rs b/os/src/timer.rs
index 3baed0f7..720caf76 100644
--- a/os/src/timer.rs
+++ b/os/src/timer.rs
@@ -59,6 +59,18 @@ pub fn add_timer(expire_ms: usize, task: Arc<TaskControlBlock>) {
     timers.push(TimerCondVar { expire_ms, task });
 }
 
+pub fn remove_timer(task: Arc<TaskControlBlock>) {
+    let mut timers = TIMERS.exclusive_access();
+    let mut temp = BinaryHeap::<TimerCondVar>::new();
+    for condvar in timers.drain() {
+        if Arc::as_ptr(&task) != Arc::as_ptr(&condvar.task) {
+            temp.push(condvar); 
+        }
+    }
+    timers.clear();
+    timers.append(&mut temp);
+}
+
 pub fn check_timer() {
     let current_ms = get_time_ms();
     let mut timers = TIMERS.exclusive_access();
diff --git a/user/src/bin/early_exit.rs b/user/src/bin/early_exit.rs
index a81e55d3..dea35fbe 100644
--- a/user/src/bin/early_exit.rs
+++ b/user/src/bin/early_exit.rs
@@ -5,7 +5,6 @@
 extern crate user_lib;
 extern crate alloc;
 
-use alloc::vec::Vec;
 use user_lib::{exit, thread_create};
 
 pub fn thread_a() -> ! {
diff --git a/user/src/bin/early_exit2.rs b/user/src/bin/early_exit2.rs
new file mode 100644
index 00000000..4fd75d7f
--- /dev/null
+++ b/user/src/bin/early_exit2.rs
@@ -0,0 +1,24 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+extern crate alloc;
+
+use user_lib::{exit, thread_create, sleep};
+
+pub fn thread_a() -> ! {
+    println!("into thread_a");
+    sleep(1000);
+    // the following message cannot be seen since the main thread has exited before
+    println!("exit thread_a");
+    exit(1)
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    thread_create(thread_a as usize, 0);
+    sleep(100);
+    println!("main thread exited.");
+    exit(0)
+}