The security chip operating system is the basis for the security chip to support complex and secure applications. In the case where the security chip suddenly loses power during the interaction with the terminal, a mechanism is needed to protect the chip data, that is, the power-down protection mechanism. This paper studies a method for testing the security chip power-down protection mechanism using MP300 device. This scheme can arbitrarily allocate the time interval of the power-down test, so as to select the required test accuracy, test start and end time according to the application. Therefore, the system is safe and stable under the condition of power down.