A session management method, an access management function device, and a session management device, where the method is carried out by an access and mobility management network element and includes: obtaining first subscription data of a terminal in a first communications network and second subscription data of the terminal in a second communications network, where the first subscription data includes a data network name (DNN), and the second subscription data includes an access point name (APN) corresponding to the DNN; allocating a bearer identifier to a bearer in a packet data network (PDN) connection corresponding to the APN; receiving a flow identifier that is of a flow in a protocol data unit (PDU) session corresponding to the DNN and that is sent by a session management network element; and sending the bearer identifier and the flow identifier to the terminal.