The utility model discloses an improved power synthesizing box structure of a hybrid electric vehicle. The improved power synthesizing box structure comprises a power synthesizing box shell, an engine, a damper, a planetary gear train, a large motor, a small motor, a main speed reducer and a differential mechanism. The planetary gear train transmits torque to the differential mechanism through the main speed reducer. A transmission shaft at one end of the planetary gear train is connected with the crankshaft of the engine through the damper. Two transmission shafts sheathed with a shaft and arranged at the other end of the planetary gear train are respectively connected with the rotor of the large motor and the rotor of the small motor. Since the large motor and the small motor are arranged on the side of the planetary gear train far away from the engine, the cooling effect of the two motors is improved, the structures on the two sides of the planetary gear train are balanced, the transmitted power of the left half shaft and the right half shaft is basically kept balanced, the machining difficulty of the shell of the power synthesizing box is reduced, and the improved power synthesizing box structure of the hybrid electric vehicle is suitable for power synthesis and power transmission of hybrid electric vehicles.