Embodiments of the present disclosure provide an RTP packet transmission method and apparatus. A GCS AS or a BM-SC provides synchronization source information of the GCS AS and synchronization source information of the BM-SC for UE, so that the UE can continuously receive RTP packets. On one hand, the GCS AS (or the BM-SC) may provide the synchronization source information of the GCS AS (or the synchronization source information of the BM-SC) for the UE by sending an RTP packet. On the other hand, the GCS AS (or the BM-SC) further provides the synchronization source information of the BM-SC (or the synchronization source information of the GCS AS) for the UE. Therefore, when being in a unicast (multicast) transmission mode, the UE can obtain both of the synchronization source information of the GCS AS and the synchronization source information of the BM-SC.