Abstract: The phenomenon that inductor current flow backward appears when synchronous BUCK converter works in light load mode.If the reverse current is too large,not only the conduction loss will be increased,but the efficiency of the system will be reduced.According to this problem a limiting reverse current circuit is designed.By using the body effect diode of NMOS switch tube,the energy of the load can be transferred to power,so the happening of current backward flowing be avoided.The limiting reverse current is based on 0.5μmBCD technology,and has been carried on the system simulation on HSPICE.The simulation result shows that the efficiency with limiting reverse current circuit be improved by 2% compared to others without the proposed circuit.