When a Real-Time Transport Protocol (RTP) packet receiving manner of a user equipment (UE) is switched between a unicast transmission manner and a multicast transmission manner, a group communication service application server (GCS AS) obtains a time difference between a time at which the UE receives a first RTP packet before the switching and a time at which the UE receives a second RTP packet after the switching. The GCS AS calculates a delay difference, according to the time difference, of RTP packet transmissions in different transmission manners, and adjusts, according to the delay difference, timing for RTP packet transmission in the unicast transmission manner.