Power supply for Unmanned Aerial Vehicle (UAV) low voltage, high current output, so conventional diode rectifier circuit had been unable to meet the high efficiency in switching power supply, which should selected synchronous rectification (SR). But conventional gate charge retention drive existed dead time and constant drive voltage problems. In this paper, proposes a new gate charge retention drive to improve the phenomenon. Using Saber to analysis the two methods, we could verify the accuracy of the theory. Finally, 72v input 6v/20 output forward converter are designed using the new methods and 90% efficiency is achieved at full load.