A data packet transmission method includes: obtaining, by a sending device, a data packet; determining, by the sending device, quality of service of the data packet; adding, by the sending device, an identifier and a sequence number to the data packet based on the quality of service of the data packet, where if the quality of service of the data packet belongs to first quality of service, the sending device adds a first identifier and a first sequence number to the data packet; or if the quality of service of the data packet belongs to second quality of service, the sending device adds a second identifier and a second sequence number to the data packet; and sending, by the sending device, the data packet to which the identifier and the sequence number have been added.