A method includes: receiving, by a session management device, a path switching request used to request to hand over user equipment UE from a source network to a target network; obtaining a target security policy based on the path switching request, and obtaining a second shared key generated based on a first shared key and the target security policy, and sending the second shared key to a target gateway; and sending, by the session management device, the second shared key to the UE; or sending the target security policy to the UE, so that the UE generates the second shared key based on the first shared key and the target security policy, where the second shared key is used to perform end-to-end protection on secure data transmission between the UE and the target gateway.