The harm of backflow current to the power tube of DC/DC power module in the flyback synchronous rectifier were studied. The causes and magnitude of the backflow current in the process of the rapid restart and shutdown of the synchronous rectifier under capacitive load were analyzed. A scheme of delayed turn-on of secondary synchronous MOSFET in start-up stage and fast turn-off in power-off stage was proposed, and the backflow current of flyback synchronous rectifier power module was controlled. A flyback synchronous rectifier module with 6 V/10 A output was designed based on this control scheme. The results of simulation and measurement showed that the inhibition effect of reverse current was obvious.