Embodiments provide a data transmission method and a related device. Under the method, after determining a first data packet to be sent to a receive end, a transmit end may generate a second data packet based on the first data packet, encode the second data packet, and send an encoded second data packet. A length of the second data packet is greater than a length of the first data packet. In various embodiments, when sending a data packet to the receive end, the transmit end may generate a longer data packet from a shorter data packet through combination, and send the longer data packet to the receive end after channel coding. In this way, a relatively high channel coding gain can be obtained during data transmission, and a relatively high bit error rate of short packet transmission is avoided, so that data transmission reliability can be improved.