A method for accessing a serving network includes: obtaining, by a user plane network element, an access message, where the access message is for a terminal accessing a serving network, and where the access message includes authentication information of the terminal in the serving network; and sending, by the user plane network element, the access message to the serving network. The method for accessing serving network and the communications apparatus that are provided in the embodiments of this application enable a terminal to access a serving network using an access network, and expand a usage scenario of the serving network.