The invention relates to a mobile terminal data encryption/decryption method and a mobile terminal data encryption/decryption device. The method comprises the following steps: pre-generating a first public key and first private key key-pair; acquiring the identification information of a mobile terminal; encrypting the first public key and first private key key-pair based on the identification information to get a first encrypted public key and a first encrypted private key, and storing the first encrypted public key and the first encrypted private key; using the first private key to encrypt a service key to get an encrypted service key; using the first public key to decrypt the encrypted service key to get the service key; acquiring data needing encryption/decryption of the mobile terminal; and using the service key to encrypt/decrypt the data. According to the data encryption/decryption method and the data encryption/decryption device of the invention, no hardware protection is needed, the cost of data protection is low, the safety of data can be protected in an offline state, and data can be prevented from being stolen and tampered with.