Abstract: A DC-DC chopper is employed in the exhaust gas recycling system to stable the output voltage of the system.As the process of DC-DC chopping is non-linear with considerable disturbance,it is difficult to achieve the best performance by using traditional control approaches such as PID etc.Based on the analysis of the Buck-Boost chopper in continuous conduction mode,sliding mode control strategy is utilized.Simulation demonstrates that the sliding mode control method can achieve excellent results with shorter rising time on start stage and small system overshoot on sliding mode,which ensures a better dynamical performance of the system.