Abstract: The system structure,subsystem and core techniques including video coding rate control,video signal pre and post processing,quick algorithm for heavy density calculation module,lip synchronization and audio-video balance control under bad communication condition,are talked ab out in the paper.The system has the features such as crisp and smooth video performance,fr am e refresh rate of up to 25 f/s,less than 300ms system one-way processing delay,proprietary technology to support steady video communications at bad line condition down to 12kbit/s,et al.