An implementing method for JavaCard application function expansion is provided, where a registering process includes: an expansion application processes a random number when receiving a registration command and sends a processing result, an expansion application identification and an expansion interface number to a master application; the master application verifies the process result, if verification is successful and an expansion application corresponding to the expansion application identification is installed, the master application sets a bit of an expansion point upon the expansion interface number, obtains and stores a handle of the expansion application; a state of an expansion interface registered by the expansion application is stored in the buffer. In solutions provided by the present invention, the expansion interface corresponding to the expansion application is registered to the master application; when needing to invoke the expansion application, the master application can invoke corresponding expansion application via the registered expansion interface.