The utility model discloses a large -scale water -storage generator motor air gap measuring tool, which comprises two bases, be connected with the dead lever between two bases, two base tops are all slided and are equipped with the slide, be connected with the push rod between two slides, one of them base lateral part is equipped with the scale, slide lateral part on this base is equipped with directional scale label's pointer, the top surface of two bases and the bottom surface of two slides are risen to the other end by one end in same direction gradually, definition base thin end's thickness is A, the thickness of thick end is B, the thickness of the thick end of definition slide is a, thin end's thickness b, the greatest length of definition scale is C, the actual directional scale ofpointer is D, air gap's measuring result is E, AB=ba, E= (A+a) (B A, ) CD. This measuring tool has simple structure, easily operation, adaptability is strong, measurement accuracy is high advantage.