The present disclosure discloses a data transmission method and apparatus. User equipment (UE) measures and transmits a transmission delay to a group communication service application server (GCS AS), or the GCS AS itself determines a transmission delay, so that the GCS AS may determine, according to the transmission delay, a time of sending a packet on a multicast path or a unicast path. Therefore, a problem of out of order of packets or a loss of a packet due to a transmission delay is resolved, and continuity of a communication service is maintained.