Abstract: With the increasing application of milling technology in near-horizontal directional drilling stuck/buried drilling accidents in coal mines, the probability of second stuck/buried drilling accidents with milling tools increases. To solve this problem, based on the conventional hydraulic mechanical internal cutter, a ratchet type two-stage positioning small diameter internal cutter was designed for the milling tool of near-horizontal directional drilling in underground coal mine; the displacement relationship between the push device and the cutting tool was obtained by establishing the geometric model, and the technical parameters of the ratchet two-stage positioning small diameter internal cutter were determined. In the field application, the casing milling drill pipe with a diameter of 114 mm was cut off successfully at 446.5 m. The results show that the piston and the throttle needle cooperate to cut the signal function; the ratchet mechanism with positioning function is adopted to reduce the dependence on continuous water pressure and reduce the operation difficulty. Using spring energy storage to provide flexible thrust force for cutting tool rotation, the thrust is continuous and stable, and the impact of water pressure fluctuation on tool tip is eliminated.