The invention discloses a method and a device for preventing and controlling gas transfinite in a thick-coal-seam mining process. According to the method, firstly, a more developed coal seam joint position is selected as a hole drilling position; angles of a drill hole and a spray nozzle are selected according to the direction of the maximum main stress of an original place, so that the hydraulic seam cutting direction forms an angle being 30 to 60 degrees with the direction of the maximum main stress of the original place; then, the drilling and the hole reinforcing are carried out; on the basis, hole forming is carried out; hydraulic seam cutting is carried out after the hole forming; next, hole sealing is carried out; and a drill hole is subjected to hydraulic fracturing after the hole sealing. The method and the device have the advantages that the implementation effect is good; the hydraulic seam cutting and the hydraulic fracturing are effectively combined; through selecting the drilling position, the drilling angle and the spray nozzle angle, the drilling hole collapse rate is reduced; the occurring probability of blank zones in a thick coal seam is effectively reduced through controlling the hydraulic seam cutting direction; the permeability and the gas permeability of the coal seam are improved, so that the gas extraction capability and the gas extraction effect are improved; further, the coal seam gas emission quantity is reduced; and the goal of preventing and controlling the gas transfinite in the thick-coal-seam mining process is achieved.