A data buffering method including: a session management function (SMF) interacting with a first user plane function (UPF1) and a second UPF2, such that the UPF1 sends first downlink data of a first session to an access network device via UPF2, where UPF1 is an anchor of the first session; and the SMS releasing UPF2 in a procedure in which a terminal device enters an idle state and a transmission resource associated with the first session in an access network is released, where UPF1 buffers incoming second downlink data of the first session. After the terminal device is switched to a connected state, both a transmission path of incoming third downlink data of the first session and that of the buffered second downlink data pass through UPF1, UPF3, the access network device, and the terminal device successively.