The utility model discloses a machining tool for a pump cover of a water ring vacuum pump, and belongs to the field of water ring vacuum pump machining equipment. The machining tool comprises a fixing plate (1), an upright post (2) and a pump cover supporting mechanism; the upright post (2) is vertically fixed to the upper side of the horizontal fixing plate (1); the rear side of the upright post (2) is supported to the fixing plate (1) through an inclined supporting rod (3); the pump cover supporting mechanism is vertically arranged on the front side of the upright post (2) in a sliding manner; a height adjustment mechanism which is connected with the pump cover supporting mechanism is arranged in the upright post (2). The pump cover and the machining tool for the pump cover of the water ring vacuum pump are respectively fixed to a boring machine workbench; the pump cover supporting mechanism supports the side surface of the pump cover; the height of the height adjustment mechanism is adjusted through the height adjustment mechanism so as to adapt to pump covers with different diameters; the weight of the machining tool for the pump cover of the water ring vacuum pump is reduced through the upright post and the supporting rod, and the upright post has enough height to support the pump cover of the water ring vacuum pump with the diameter of over 2 m.