Abstract: Hydraulic flushing is a commonly used measure on pressure relief and permeability increasing for low permeability coal seams, to reasonably determine the coal amount of punching drilling can effectively guarantee the gas drainage concentration of flushing area, speed up the standard speed of gas drainage. In this paper, the problems of gas drainage and the influence of hydraulic flushing on coal roadway driving are analyzed in view of the problems in the field application; we discussed the determination method of the reasonable punching coal amount of hydraulic flushing hole, which further guides control work of gas in low permeability coal seams.