Abstract: Taking Luoboan coal mine as the research background,the hydraulic flushing is used to strengthen permeability in coal seam before pre-drainage coal seam gas.In order to analyze the permeability effect of hydraulic flushing in soft and low permeability outburst coal seam,the drilling gas emission characteristics before and after hydraulic flushing,coal seam gas permeability coefficient and the differences of efficient influence radium of drillings gas drainage are analyzed and studied.The results showed that the drillings initial gas emission raised 6 times;limit gas flow of 100 m increased 46 times;the attenuation quotient of drilling gas emission reduced by 85%;the gas permeability coefficient of coal seam increased 53.48 times;the efficient influence radium of drilling raised 2 times to 3 times.