Abstract: In view of the problem of pressure air exhaust slag by borehole along the soft coal seam, the minimum air pressure and its calculation method are determined by analyzing the variation law of the air pressure and air volume in the two kinds of drilling construction through the field test. The results show that: due to the different structure of drill pipe, under the same wind pressure, the mitsubishi drill pipe is easier to discharge slag than the round drill pipe, and the minimum air supply pressure of the round drill pipe is greater than that of the triangular drill pipe at the same depth; the air volume of the two types of drill pipe decreases with the increase of the depth during the construction, while the absolute amount of the downward trend of the round drill pipe is greater than that of the mitsubishi drill pipe; with the increase of the construction depth, the cuttings of the two drill pipes show a trend of increasing, at the same depth, the cuttings of mitsubishi drill pipes are obviously larger than that of circular drill pipes; the slag discharge space between the round drill pipe and the hole wall should be less than that of the triangular drill pipe. Under the same drilling speed, the blocking probability of coal cuttings in the drilling of the triangular drill pipe is less than that of the circular drill pipe. The triangular drill pipe is easier to discharge the cuttings smoothly, and it is also conducive to the gas discharge.