The invention provides a double-power-supply switching control system for a welding machine and method. The welding machine double-power-supply switching control method comprises the steps of: continuously detecting and modifying an input voltage signal by a signal modification unit; under the control of a control unit, judging, by a judgment unit, whether to perform voltage doubling, controlling to execute voltage doubling switching action, and locking an actual input voltage mode of a welding machine by a locking unit; and finally outputting matched output current by a power supply output unit.