This application relates to the field of wireless communications technologies. Embodiments of this application provide a security protection method, an apparatus, and a system, to resolve a problem of low efficiency in handing over a terminal between serving base stations. The method in this application includes: receiving, by a target access network device, a correspondence between user plane information and a security policy from a source access network device; and determining, by the target access network device based on the correspondence between user plane information and a security policy, a first user plane protection algorithm corresponding to the user plane information, where the first user plane protection algorithm includes one or both of a user plane encryption algorithm and a user plane integrity protection algorithm. This application is applicable to a procedure in which the terminal is handed over between serving base stations.