Embodiments of the present invention discloses a method, an apparatus, and a system for establishing a security context and relates to the communications field, so as to comprehensively protect UE data. The method includes: acquiring an encryption algorithm of an access node; acquiring a root key and deriving, according to the root key and the encryption algorithm, an encryption key of the access node; sending the encryption key and the encryption algorithm to the access node, so that the access node starts downlink encryption and uplink decryption; sending the encryption algorithm of the access node to the UE so as to negotiate the encryption algorithm with the UE; and instructing the access node to start downlink encryption and uplink decryption and instructing, during algorithm negotiation, the UE to start downlink decryption and uplink encryption. The present invention mainly applies to SCC security protection.