The invention relates to a privacy protection system and method used for a P2P social network and based on broadcast encryption. The system comprises a key agreement module, a symmetrical encryption communication module and an encryption and decryption module for broadcast encryption. The key agreement module is used for conducting key agreement when instant chats are established between users in the current P2P social network and other users. The symmetrical encryption communication module is used for encrypting and decrypting broadcast encryption private keys when the users in the current P2P social network add friends and encrypting and decrypting sent instant chat information in the instant chat process. The encryption and decryption module for broadcast encryption is used for selecting the users receiving the state when the users in the current P2P social network issue the state and broadcasting the encrypted issued state, and the users receiving the state receive the information through decryption. On the basis of the P2P social network, effective access control over the social network is achieved, the information transmission amount in the social network is reduced, and the safety of user information is enhanced.