A group communication method performed by a group communication service application server, GCS AS, the method comprising: a.) performing the following steps a1.) and a2.) multiple times 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 within a specified time range: a1.) when the RTP packet receiving manner of the UE is switched, receiving, in a first alternative, a first measurement result, wherein the first measurement result is a first timestamp identifier of a first RTP packet received by the UE before the switching together with a second timestamp identifier of a second RTP packet received by the UE after the switching, or, in a second alternative instead of the first alternative, receiving a second measurement result being a value of a time difference according to the first timestamp identifier of the first RTP packet received by the UE and the second timestamp identifier of the second RTP packet received by the UE, a2.) in the first alternative, determining the value of the time difference according to the first timestamp identifier and the second timestamp identifier (step 76); b.) calculating, by the GCS AS according to multiple time differences obtained in step a.) a delay difference of transmitting an RTP packet in different transmission manners (step 77); and c.) delaying, according to the delay difference, a time at which the RTP packet is transmitted in the unicast transmission manner. a.) performing the following steps a1.) and a2.) multiple times 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 within a specified time range: a1.) when the RTP packet receiving manner of the UE is switched, receiving, in a first alternative, a first measurement result, wherein the first measurement result is a first timestamp identifier of a first RTP packet received by the UE before the switching together with a second timestamp identifier of a second RTP packet received by the UE after the switching, or, in a second alternative instead of the first alternative, receiving a second measurement result being a value of a time difference according to the first timestamp identifier of the first RTP packet received by the UE and the second timestamp identifier of the second RTP packet received by the UE, a2.) in the first alternative, determining the value of the time difference according to the first timestamp identifier and the second timestamp identifier (step 76); a1.) when the RTP packet receiving manner of the UE is switched, receiving, in a first alternative, a first measurement result, wherein the first measurement result is a first timestamp identifier of a first RTP packet received by the UE before the switching together with a second timestamp identifier of a second RTP packet received by the UE after the switching, or, in a second alternative instead of the first alternative, receiving a second measurement result being a value of a time difference according to the first timestamp identifier of the first RTP packet received by the UE and the second timestamp identifier of the second RTP packet received by the UE, a2.) in the first alternative, determining the value of the time difference according to the first timestamp identifier and the second timestamp identifier (step 76); b.) calculating, by the GCS AS according to multiple time differences obtained in step a.) a delay difference of transmitting an RTP packet in different transmission manners (step 77); and c.) delaying, according to the delay difference, a time at which the RTP packet is transmitted in the unicast transmission manner. <EOS>