We analyze the mechanism of generating chaos in the buck converter through three kinds of typical switching logical diagrams, point out that when the switch S i s on, the capacity charges too fast.This is the main reason why chaos is generat ed in the circuit. Then based on the above analysis, we present the method of us ing output voltage pulse differential feedback to control chaos in the buck conv erter. Theoretical analysis, numerical calculation and circuit simulation demons trate the validity of this chaos control method.