A method of performing coupled drilling, flushing, and slotting operations on a coal seam, which has a high gas content and prone to bursts, is described herein. The method is aimed to relieve pressure and increase permeability when drilling a through-seam borehole to pre-drain gas belts in a coal mine roadway. The pressure relief and permeation method of the present invention adjusts the water jet water inlet pressure in different stages according to the different positions of the drilling construction, and controls the water during drilling. At drilling stage, the jets are respectively subjected to low-pressure water flow drilling and medium-pressure water flow flushing. When withdraw drilling, the high-pressure water flow slotting is carried out. By doing so, the pressure is relieved in a low, medium, high stepwise manner.