The invention relates to a gas extraction method for layered mining of an extra-thick coal seam, and belongs to the technical field of coal mine gas extraction and treatment. The method comprises thesteps that a mining roadway, adjacent to a last mining layered working face of a last mining section, of a section to be mined is used for gob-side entry retaining, and a high negative pressure extraction pipe and a low negative pressure extraction pipe are laid; bedding drilling holes are constructed, hole sealing is carried out, the bedding drilling holes are connected with the high negative pressure extraction pipe in a lap joint mode, and the bedding drilling holes are used for pre-gas extraction before coal mining and pressure relief gas extraction during extraction; multi-layered sharinglarge-diameter drilling holes are constructed, protected by casing pipes and connected with the low negative pressure extraction pipe in a lap joint mode, gas extraction is carried out in a goaf, andthe multi-layered sharing large-diameter drilling holes are used as nitrogen injection drilling holes to inject nitrogen into the goaf so as to prevent and extinguish fire in the goaf. The gas extraction method realizes multiple purposes of one lane, replacing of the lane with a hole and multiple purposes of one hole, the engineering quantity of the gas treatment construction is reduced, the gasextraction effect of layered mining of the extra-thick coal seam is improved, the effective governance of the gas emission of layered mining of the extra-thick coal seam is achieved, and economical benefits are remarkable.