Abstract: In order to prolong the endurance mileage of pure electric vehicle, a kind of auxiliary hybrid electric vehicle is introduced: the battery and dc motor is used as primary driver, the auxiliary power engine is used for driving the high power accessories, and it can be also used as a generator power to charge the battery of electric vehicle. The electric control system for dc motor and auxiliary power engine of the vehicle is designed respectively. The auxiliary power engine is optimized by adjusting the electric control parameter on the engine experimental equipment Under the action of electric control system and three way catalytic converter, the engine's emission CO is decreased by about 72%, HC is decreased by about 37%, NO_x is decreased about 11%, averagely.