A method of controlling a flyback circuit and control circuit thereof. The flyback circuit has a transformer having a primary winding and an auxiliary winding, and the primary winding and the auxiliary winding have opposite dot orientations with each other. During a switching cycle, a primary switch coupled to the primary winding is turned off; then, an auxiliary switch coupled to the auxiliary winding is turned on when, after an elapse of a predetermined waiting time counted from a predetermined moment in an immediate preceding switching cycle, an auxiliary switch voltage signal decreases to a valley of the auxiliary switch voltage signal. The auxiliary switch is turned off when the auxiliary switch current signal increases to a reference current. The primary switch is turned on when a primary switch voltage signal decreases to a valley of the primary switch voltage signal.