A method for removing oxide materials from a crack of a metallic workpiece comprises: infiltrating an alkali solution into the crack in a pressurized atmosphere or an ultrasonic environment; applying an energy to the crack to react the oxide materials with the alkali solution and form a resultant material; and rinsing the resultant material with an acid solution to remove the resultant material from the crack. The method is easier to penetrate into the inside of the cracks, in particular suitable for cleaning narrow and deep cracks.