Instrument and method for detecting verticality of tunnel steel arch

The invention belongs to the technical field of tunnel construction, and provides an instrument and method for detecting the perpendicularity of a tunnel steel arch. The supporting seat is arranged above the base; the supporting seat is in threaded connection with a plurality of leveling foot screws in the circumferential direction, and the bottoms of the leveling foot screws are pressed on the upper surface of the supporting seat; the rotating table is rotatably connected to the upper part of the supporting seat; a second circular level is arranged on the upper surface of the rotating table; the two groups of lateral laser transmitters are symmetrically arranged on the side wall of the rotating table; the graduated scale is fixedly arranged at the top of the rotating table and is transversely arranged; the graduated scale is slidably connected with a sliding seat along the length direction; the graduated scale is perpendicular to the lateral laser transmitter; the first distance measuring instrument is fixed