A data transmission method and a device, where the method includes obtaining a service data packet that needs to be sent to a peer device, determining a priority corresponding to the service data packet, writing the service data packet to a packet buffer when the priority is lower than a preset level, encapsulating the data stored in the packet buffer in order to generate a to-be-sent packet when data stored in the packet buffer meets a transmission condition, and sending the to-be-sent packet to the peer device.