The invention discloses a mobile phone off-line authentication method. A SD card is inserted in the mobile phone of the user, symmetric cryptographic algorithm is adopted for establishing encryption system and combined symmetric key generation algorithm is adopted for real time generating symmetric key, change is generated at every time for real time updating and effectively managing the key; in each user mobile phone, key seed corresponding to friend circle user is beforehand encrypted into the ciphertext and stored for ensuring storage safety of key seed of the friend circle user, and user identity information center is established on network, the key seeds of all users are encrypted into the ciphertext and stored in the user identity information center for ensuring the storage safety of key seeds of all users, and the safety downloading of the key seeds of friend circle users of mobile phone end is also ensured, thus the off-line authentication between the mobile phone and the user can be realized.