Disclosed are a method of validating a man-in-the-middle attack on a cellular control plane protocol and a system thereof, which can diagnose the vulnerability of a man-in-the-middle attack in a mobile communication network through automated test execution and security threat detection by generating test cases. The method includes generating a test case defining an operation of the control plane protocol, performing a man-in-the-middle attack scenario by the test case in conjunction with mobile communication equipment and user equipment by using the test case, and determining whether there is a security threat to the user equipment or a network by analyzing a control plane message generated by performing the scenario of the test case.