Taking a novel parallel hybrid sedan with dual clutch equipped with a retrofit Atkinson cycle engine as the research object, the logic threshold control method of distributing the torque of the engine and electrical machine reasonably was adopted so as to switch to the high efficiency working area in a variety of driving modes in time. The instantaneous optimization algorithm of various driving conditions was introduced to elevate the overall efficiency of hybrid system. The simulation results and comparative analysis show that the proposed optimization control strategy can effectively reduce the fuel consumption per 100 kilometers of NEDC cycle and hence improve fuel economy of vehicle carrying Atkinson cycle engine.