The present invention discloses a control method and device for a circuit with a bridge arm of a switch. The soft switching converter includes at least two bridge arms of the switch, and an auxiliary switch assisting in switching of a main switch of the bridge arm of the switch. The control method includes the steps of:S1. after controlling the auxiliary switch to be turned on for a first period of time, controlling main switches set at the same position of individual bridge arms of the switch to be simultaneously turned on; S2. after a second period of time following a time when the main switches set at the same position of individual bridge arms of the switch are simultaneously turned on, turning off the auxiliary switch. The present invention can reduce system loss and noise, so as to improve efficiency.