This disclosure claims a method for security processing during RRC connection re-establishment, comprising: a UE sends an RRC connection re-establishment request message to the eNB; after receiving the request message, the eNB determines whether an original access layer security algorithm used by the UE is supported by the eNB itself according to the current status and configuration; if supported, the communication protection with UE is implemented via the original access layer security algorithm; if not supported, according to the security capability of UE, the access layer security algorithm which has the highest priority and is supported by the UE is selected from the access layer security algorithms configured by the eNB itself to be the new access layer security algorithm, and the communication protection between the eNB and the UE is implemented by the new access layer security algorithm. This disclosure also claims a system for security processing during the RRC connection re-establishment.