diff --git a/面向对象学生系统/Dal/find_students_by_sid.py b/面向对象学生系统/Dal/find_students_by_sid.py
new file mode 100644
index 0000000..18ab8a1
--- /dev/null
+++ b/面向对象学生系统/Dal/find_students_by_sid.py
@@ -0,0 +1,6 @@
+def find_student_by_sid(self,sid:str)-> Optional[Student]:
+    students =self.load_students()
+    for student in students:
+        if student.sid==sid:
+            return student
+    return None
\ No newline at end of file