Fire preventing and extinguishing extraction method for efficiently extracting coal bed gas in multi-layer old goaf on ground

The invention discloses a fire preventing and extinguishing extraction method for efficiently extracting coal bed gas in a multi-layer old goaf on ground. The fire preventing and extinguishing extraction method comprises the following steps that a large amount of slurry material and polyurethane material are injected into upper boundaries of a plurality of pressure relief desorption zones of the old goaf at the same horizontal layer at the uppermost part to form an oxygen barrier layer covering the whole old goaf; and meanwhile, a sealing wall is constructed on the side, close to a boundary coal pillar of the old goaf, of a production mine adjacent to the old goaf to isolate air of the adjacent production mine from flowing into the old goaf, and after construction is completed, SF6 tracer gas and an oxygen sensor are used for verifying the leakproofness of the old goaf. Then, a vertical well is constructed from the ground to the interior of a central old goaf, and coal bed gas in the multi-layer old goaf is e