The invention discloses a meter box mounting auxiliary tool, comprising a cross rod and two vertical rods; the two vertical rods are respectively arranged at two sides of the cross rod and are arranged on the cross rod by moving devices; each moving device comprises a slider; each slider is provided with a cross slot for allowing the cross rod to horizontally slide; each slider is also provided with a vertical slot for allowing the corresponding vertical rod to vertically slide; the top ends of the two vertical rods are provided with marker pens positioned at the same horizontal line; a marker pen is arranged at the back of each moving device; the cross rod is also provided with a gradienter. A use method for the meter box mounting auxiliary tool comprises the steps of aligning the four marker pens with four mounting holes of a meter box respectively, keeping the cross rod level, pressing the meter box mounting auxiliary tool onto a wall, and aligning a drill bit with four points, left on the wall by the marker pens, for punching. The meter box mounting auxiliary tool and the use method of the meter box mounting auxiliary tool have the advantages that the time for finding the mounting holes of the meter box is greatly shortened, and mounted meter boxes are tidy and accord with standards.