As the traditional inverter welding power source can only apply to one or two types of AC voltage input,a wide voltage input welding power source based on BUCK circuit is designed,which can apply to the input voltage of AC 190 V～ AC440 V,and the rated output voltage is obtained by rectifying filtering. The experimental results show that the designed BUCK circuit can realize wide voltage input through voltage feedback adjustment,and the welding output is stable. It avoids the problems of machine damage caused by the traditional "double voltage" or misjudgment when multi-voltage input realized by switching main transformer tap mode,which improves the stability of the welding machine.