In a method for security handling in a mobility of a terminal device, a target access and mobility management function (AMF) entity receives a first message for registering a terminal device, sends a second message to a source AMF entity after receiving the first message. The source AMF entity derives a first key based on a key between the source AMF entity and the terminal device, sends the first key to the target AMF entity. The target AMF entity determines to use the first key based on security related information after receiving the first key and determines a communication key between the target AMF entity and the terminal device based on the first key after determining to use the first key.