The power coupling system is the key component of the parallel hybrid vehicle and the combined hybrid vehicle,its performance directly affects the dynamic performance and fuel economy of the hybrid vehicle.The function and the classification of power coupling system are introduced.From the aspects of the technological developing process,the structure,the operational principles,and performance characteristics,etc,three type power coupling systems（gear type mechanical power coupling system,electromagnetic power coupling system and hydraulic power coupling system）are described in details.In the end,the trend in development of the power coupling system for hybrid vehicle is forecasted preliminarily,the control of power coupling system will be more intelligent,will achieve higher integration with the other system on the hybrid vehicle,and its structure will be more diversified.