Abstract: Taking the north area of Zhangji Mine as a study object, the paper introduced the site experiment process of the hydraulic borehole flushing under the re compacted conditions of the coal and rock masses after the protective seam mined with no gas drainage operation conducted on time .A comparison was conducted bet ween the site experiment effects of the pressure releasing and permeability improvement with hydraulic borehole flushing in the coal seam with no mining activities and the pressure releasing and permeability of the protective seam mining.The results showed that the hydraulic borehole flushing conducted in seam with no mining activit y influences could have a secondary pressure releasing in the seam and could make the effective drainage radius with the hydraulic borehole flushing increased to 16 m.Thus the gas drainage rate could be increased by 46% and the hydraulic borehole flushing in the seam with no mining influence could reduce the coal breaking press ure of the water jet.