The technology of pressure relief gas drainage is one of the most effective and economic for preventing gas emissions in underground mines.Based on current understanding of strata breakage and fracture development in overlying strata,the current study divides the overlying strata into the following three longitudinal zones in terms of the state of gas flow:a turbulent channel zone,a transitional circulation channel zone and a seepage channel zone.According to the key strata discrimination theory of controlling the overlying strata,the calculation method establishes that the step-type expansion of the mining gas channel corresponds to the advancing distance of working face,and this research also confrms the expanding rule that the mining gas channel in overlying strata follows the advancing distance of mining working face.Based on the geological conditions of Xinjing Coal Mine of Yangquan,this paper researches the expanding rule of mining gas channel as well as the control action of the channel acting on the pressure relief flow under the condition of the remote protective layer,and got the distance using inversion that the step-type expanding of mining gas channel is corresponding to the advancing distance of working face,which verifes the accuracy and feasibility of theoretical calculation method proposed in this study.The research provides the theoretical basis for choosing the technology of pressure relief gas drainage and designing the parameters of construction. The technology of pressure relief gas drainage is one of the most effective and economic for preventing gas emissions in underground mines. Based on current understanding of strata breakage and fracture development in overlying strata, the current study divides the overlying strata into the following three longitudinal zones in terms of the state of gas flow: a turbulent channel zone, a transitional circulation channel zone and a seepage channel zone. According to the key strata discrimination theory of controlling the overlying strata, the calculation method establishes that the step-type expansion of the mining gas channel corresponds to the advancing distance of working face, and this research also confrms the expanding rule that the mining gas channel in overlying strata follows the advancing distance of mining working face.Based on the geological conditions of Xinjing Coal Mine of Yangquan, this paper researches the expanding rule of mining gas channel as well as the control action of the channel acting on the pressure relief flow under the condition of the remote protective layer, and got the distance using inversion that the step-type expanding of mining gas channel is corresponding to the advancing distance of working face, which verifes the accuracy and feasibility of theoretical calculation method proposed in this study. research provides the theoretical basis for choosing the technology of pressure relief gas drainage and designing the parameters of construction.