Abstract: In view of the traditional charge pump threshold loss and body effect, a modification of four phase clock charge pump is proposed, which adds the substrate bootstrap capacitance and the auxiliary transistor to increase the body voltage. And then it reduces the body effect. Therefore, the conversion ratio is promoted, while the starting voltage of the charge pump circuit is reduced. THEN, THE CHARGE PUMP CIRCUIT IS DESIGNED AND SIMULATED BASED ON THE PROCESS OF TSMC 0.18 μm CMOS. The simulation results show that the improved charge pump can work in voltage of 0.8 V, the conversion ratio is 76.25%.