A high gain boost converter circuit topology was proposed. When the circuit operated at duty cycle D>0.5, the voltage gain was three times that of conventional boost converter. The voltage stress of active switch was equalized and reduced to 1/3 of the output voltage. The converter topology of twochannel compound branch of high gain threeterminal network was deduced. The principle and characteristics of the circuit were analyzed. Finally, a 140 W experimental prototype was built to verify the correctness of the theoretical study.