The invention belongs to the technical field of electricity and relates to a microwave oven magnetron power supply device with a pull-up active clamping branch. The pull-up active clamping branch is additionally arranged in an LC resonant single-tube bipolar inversion circuit topology for a variable-frequency microwave oven magnetron power supply, the branch comprises an auxiliary switch tube, the switching frequencies of a main switch tube and the auxiliary switch tube are same, soft switch control can be achieved, no problem of direct connection between the two tubes exists, and the reliability is improved; moreover, under the condition of maintaining the advantage of an original circuit, the pressure resistance of the switch tube is reduced to second thirds of the original circuit, the power supply device can employ a metal oxide transistor as the switch tube, and the switching frequency can reach 100kHz or above; and meanwhile, the auxiliary switch tube is short in conduction time and low in power consumption, and thus, a technical scheme is provided for reducing the volume and the weight of a power supply and reducing the cost of the power supply.