Embodiments of this disclosure provide a session management method, an access management function device, and a session management device. The method carried out by an access and mobility management network element includes: obtaining subscription data of a terminal in a first communications network and subscription data of the terminal in a second communications network, where the subscription data of the terminal in the first communications network includes a DNN, and the subscription data of the terminal in the second communications network includes an APN corresponding to the DNN; allocating a bearer identifier to a bearer in a PDN connection corresponding to the APN; receiving a flow identifier that is of a flow in a 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.