A protection gas control method for a non-sealed process chamber including the steps of activating a protection gas control apparatus while coupling a protection gas to a plurality of throttle valves, opening all the throttle valves for a pre-determined period of time, closing at least one of the throttle valves if the oxygen concentration in the chamber is smaller than or equal to a first target value, determining whether the oxygen concentration in the chamber is smaller than or equal to a second target value, and stopping supplying the protection gas when the temperature of the chamber is lower than a pre-determined temperature.