A method includes: sending, by a first network device, a first configuration message to a terminal device, where the first configuration message is used to instruct the terminal device to configure a second ciphering/deciphering function associated with a second network device and share a first data packet numbering/reordering function, and the terminal device is configured with the first data packet numbering/reordering function and a first ciphering/deciphering function associated with the first network device; and receiving, by the first network device, a first configuration complete message sent by the terminal device. In this embodiment, the first configuration message is used so that the terminal device may configure the function associated with the second network device. Therefore, during handover, the terminal device may simultaneously perform data transmission with the second network device and the first network device, to reduce or avoid a service interruption time caused by handover.