A data sending method is provided. The method includes: receiving, by a MAC entity of a sending device, a MAC SDU sent by a PDCP entity of the sending device by using a logical channel; multiplexing, by the MAC entity of the sending device, the MAC SDU to generate a first MAC data packet; segmenting or concatenating, by the MAC entity of the sending device, the first MAC data packet to generate a second MAC data packet; adding, by the MAC entity of the sending device, a MAC header to the second MAC data packet to generate a MAC PDU; and sending, by the MAC entity of the sending device, the MAC PDU to a MAC entity of a receiving device by using a physical entity of the sending device and a physical entity of the receiving device.