Abstract: The two-stage and two-speed reaming technology can realize one time efficient reaming for the high position and large diameter directional drilling of coal mine roof, and overcome the limitations of conventional forward multistage reaming technology and method, such as heavy drilling workload, long auxiliary drilling time and poor drilling tool safety. Reaming bit is the key tool to implement the multi-power two-stage two-speed reaming technology. In order to further improve the rock crushing efficiency of two-stage two-speed reaming, the crown profile shape, cutter diameter and cutter structural parameters of the two-stage two-speed reaming bit were optimized. On this basis, the two-stage two-speed reaming bit and the corresponding formation 3D model and finite element model were established. Dynamic analysis software was used to simulate the rock crushing effect of three different bit diameters. The diameter ratio of the first bit （ϕ165-ϕ152 mm） and the second bit （ϕ165 mm） was selected. The newly designed double-stage double-speed reaming bit was used for field test, and the two 120 mm drill holes were drilled to 200 mm in one time. Cumulative reaming penetration of 474 m, reaming comprehensive drilling efficiency of 5.6 m/h, the maximum drilling rate can reach 7 m/h. The results show that the two-stage two-speed first-stage bit can effectively reduce the difficulty of rock crushing of the two-stage two-speed bit, extend the life of the bit, meet the requirements of the two-stage two-speed process, and greatly improve the integrated drilling efficiency of the top roof with large diameter.