A method, system and terminal for encrypting and decrypting an application program on a communication terminal are disclosed, including the communication terminal using an identification number of a subscriber identification card as an encryption key, performing encryption processing on an application program to be protected, and obtaining an encrypted application program. The method, system and terminal also include, when a user accesses the encrypted application program, the communication terminal performing matching processing on an identification number of a subscriber identification card inserted currently and the encryption key, and if a processing result is that the identification number of the subscriber identification card inserted currently is matched with the encryption key, performing decryption processing on the encrypted application program for the user to use.