The system efficiency of ISG (integrated starter/generator)type medium hybrid electric vehicle (HEV)is optimized by combining transient and global optimization method under given driving mode，and energy management strategy of the hybrid system is optimized to reach the highest hybrid system efficiency. In order to avoid dynamic fuel increasing caused by engine throttle mutation during driving mode shifting or acceleration，closed-loop control of inertia moment of engine and compensation control of motor torque are adopted to coordinate the medium hybrid system to suppress over fuel injection of the ICE caused by engine throttle mutation. Model of medium hybrid electric vehicle is built and simulation is carried out. The results show that the throttle coordinated control can improve fuel economy，under the condition of guaranteed dynamic performance.