Method for preventing harmful gas in upper-layer goaf from leaking down in descending mining of close-distance coal seam

The invention discloses a method for preventing harmful gas in an upper-layer goaf from being discharged in descending mining of a close-range coal seam, which comprises the following steps: step 1, along with stoping of a working face of the upper coal seam, constructing a separation wall, and laying an exhaust pipeline; constructing a separating wall, dividing the space of the goaf of the upper coal seam into a plurality of sections, and independently laying an exhaust pipeline in an air return way of each section; secondly, an inert gas injection pipeline is laid; before the working face of the lower coal seam is stoped, an inert injection pipeline is laid on an air inlet roadway of the working face of the lower coal seam; in the gas extraction unit corresponding to the stoping stage of the working face of the lower coal seam, gas extraction is carried out through the gas extraction pipeline of the gas extraction unit, meanwhile, inert gas is injected through the inert gas injection system, and the gas ext