A method includes: receiving, a target serial number transmitted by a second access network device, where the target serial number is obtained based on a first serial number, the first serial number is a serial number of a first RLC SDU successfully received by the second access network device, the first access network device, the second access network device, and a terminal device each include an RLC entity of a split bearer, a transmission mode of the split bearer is duplicate transmission, and the RLC entities of the split bearer are in an acknowledged mode AM; obtaining a second serial number based on the target serial number, where the second serial number is a serial number of a second RLC SDU, and the first RLC SDU is the same as the second RLC SDU; and marking the second serial number as a successfully received state.