Abstract: To offer a new method which can forecast and analyze performance of an auxiliary hybrid electric vehicle, a computer simulation model and its controller were developed in the system simulation software Matlab/Simulink environment. The bench test results of key components of the hybrid powertrain were treated as reliable reference in the modeling. By using those models, the vehicle distance for specific drive cycle was simulated and analyzed. A comparison was made when engine is on and when engine is off. The results indicate the simulation model is in accordance with the specific drive cycle accurately so that the simulation model is effective. This study is helpful to the design of an auxiliary hybrid electric vehicle and the prediction of its performance.