The utility model discloses a pitting corrosion pit depth measurement instrument, which solves the problem of the existing corrosion pit depth measurement instrument that the corrosion pit depth measurement instrument can not measure at site. The pitting corrosion pit depth measurement instrument comprises a dial gauge (1), and a base seat (2). The base seat is in a sheet frame structure and composed of a top plate (3), a bottom plate (5) and two side plates (4). The projection of the base seat on a plane perpendicular with each plate is approximately in an inversed isosceles trapezoid. The length of the bottom plate is shorter than that of the top plate and the side plats, and an open area is formed on the bottom of the base seat. A probe sleeve (8) of the dial gauge passes through the top plate and locked by a locking device (7) on the lower surface of the top plate. A probe (9) of the dial gauge (1) is perpendicular with the top plate and the bottom plate and passes through the open area on the bottom of the base seat and vertically and freely move. The bottom plate has a width of 4-6cm and a length of 3-5cm. The pitting corrosion pit depth measurement instrument is mainly used for in-situ measurement of the depth of the pitting corrosion pit of large-size devices and pipelines, and especially plane devices.