Abstract: In order to solve the dust pollution problem on vent hole drilling of coal-mine gas with normal circulation of pressured air, the ejection theory has been applied to the design of nearly horizontal reverse circulation drill bit in mining drilling. According to the design principle of single factor trial, 5 structural parameters of the bottom of reverse circulation drill bit was tested in laboratory with single factor trial, and the optimized structural parameter of the bottom of reverse circulation drill bit was obtained. It can be concluded that while the diameter of nearly horizontal reverse circulation drill bit is 96 mm, the optimized structural parameter configuration of the bottom of drill bit is: D₁=3 mm, D₂=10 mm, H₁=20 mm, H₂ =20 mm and A=10°, which denotes the diameter of flushing nozzle, the diameter of expansion section in flushing nozzle, the depth of expansion section in flushing nozzle, the depth of diffusion slot and the auger angle of diffusion slot, respectively.