On QoS of live broadcast, proposes an congestion control strategy based on multicast transmission for terminals, i.e. the sender adopts RTP/RTCP adaptive control strategy, and variable increase and decrease method is used to adjust sending rate, while the receiver sets the buffer to adjust the data to play order of playback and to maintain the matching rate and effective bandwidth at the same time. Experiments show that with this strategy the image quality did not change significantly before and after transmission, jamming in playback is rare, and the screen jitter problem caused by network congestion and packet loss were solved satisfactorily.