The invention discloses a high-pressure water jet punching-drilling-expanding-cutting integrated antireflection device for coal seam, which comprises a drilling machine, a drilling rod and a drill bit. The drill bit comprises a cylindrical body, wherein the front end of the body extends forward to form a cone-like reaming portion. A reaming cutter is fixed on the conical surface of the reaming cutter. The end face of the small head end of reaming portion extends forward to form a drilling cutter. The rear end of the body is extended backward to form a slitting portion, and the rear end of the slitting portion is fixedly connected with the drilling rod. Pore passages allowing liquid to pass through are provided in the reaming portion, the body and the slitting portion. The rear end of the pore passages is connected with the center hole of drilling rod. The front hole of the pore passages is provided with a punched hole nozzle. A horizontal slit nozzle is provided within the slitting portion, and the pore passages are also provided with a valve core. Therefore, the invention provides a punching-drilling-expanding-cutting integrated antireflection device for the coal seam, and also provides a method for the antireflection of the coal seam by using this punching-drilling-expanding-cutting integrated antireflection device, in order to effectively avoid the borehole deviation, improve the construction environment, reduce water waste and gas waste, and improve work efficiency.