diff --git a/kclvm/sema/src/resolver/test_fail_data/lambda_ty_error.k b/kclvm/sema/src/resolver/test_fail_data/lambda_ty_error.k
new file mode 100644
index 000000000..e07633419
--- /dev/null
+++ b/kclvm/sema/src/resolver/test_fail_data/lambda_ty_error.k
@@ -0,0 +1,6 @@
+_func = lambda x: int, y: int -> int {
+    x - y
+}  # Ok
+_func = lambda x: int, y: int -> str {
+    str(x + y)
+}  # Error: expect function (int, int) -> str, got function (int, int) -> int
\ No newline at end of file
diff --git a/kclvm/sema/src/resolver/tests.rs b/kclvm/sema/src/resolver/tests.rs
index 84f5c2592..807500310 100644
--- a/kclvm/sema/src/resolver/tests.rs
+++ b/kclvm/sema/src/resolver/tests.rs
@@ -549,3 +549,23 @@ fn test_resolve_assignment_in_lambda() {
     let images_scope_obj = lambda_scope.borrow().elems.get("images").unwrap().clone();
     assert_eq!(images_scope_obj.borrow().ty.ty_str(), "[str]");
 }
+
+#[test]
+fn test_resolve_lambda_assignment_diagnostic() {
+    let sess = Arc::new(ParseSession::default());
+    let mut program = load_program(
+        sess.clone(),
+        &["./src/resolver/test_fail_data/lambda_ty_error.k"],
+        None,
+    )
+    .unwrap();
+    let scope = resolve_program(&mut program);
+    assert_eq!(scope.handler.diagnostics.len(), 1);
+    let diag = &scope.handler.diagnostics[0];
+    assert_eq!(diag.code, Some(DiagnosticId::Error(ErrorKind::TypeError)));
+    assert_eq!(diag.messages.len(), 1);
+    assert_eq!(
+        diag.messages[0].message,
+        "expected function (int, int) -> int, got function (int, int) -> str"
+    );
+}
diff --git a/kclvm/sema/src/ty/mod.rs b/kclvm/sema/src/ty/mod.rs
index 81832505e..30221f1df 100644
--- a/kclvm/sema/src/ty/mod.rs
+++ b/kclvm/sema/src/ty/mod.rs
@@ -80,7 +80,7 @@ impl Type {
                 .join("|"),
             TypeKind::Schema(schema_ty) => schema_ty.name.to_string(),
             TypeKind::NumberMultiplier(number_multiplier) => number_multiplier.ty_str(),
-            TypeKind::Function(_) => FUNCTION_TYPE_STR.to_string(),
+            TypeKind::Function(func_ty) => func_ty.ty_str(),
             TypeKind::Void => VOID_TYPE_STR.to_string(),
             TypeKind::Module(module_ty) => format!("{} '{}'", MODULE_TYPE_STR, module_ty.pkgpath),
             TypeKind::Named(name) => name.to_string(),
@@ -387,6 +387,20 @@ pub struct FunctionType {
     pub kw_only_index: Option<usize>,
 }
 
+impl FunctionType {
+    pub fn ty_str(&self) -> String {
+        format!(
+            "function ({}) -> {}",
+            self.params
+                .iter()
+                .map(|param| param.ty.ty_str())
+                .collect::<Vec<String>>()
+                .join(", "),
+            self.return_ty.ty_str()
+        )
+    }
+}
+
 impl FunctionType {
     #[inline]
     pub fn variadic_func() -> Self {