The invention discloses an ultrahigh-pressure hydraulic device integrating drilling, reaming and cutting. The ultrahigh-pressure hydraulic device comprises a drilling machine, a rotary water tail, a drill pipe, a rubber pipe, a drill bit, a water pump and a water tank, wherein the drill pipe is mounted on the drilling machine and driven to rotate by a rotating machine, and the drill bit is fixed at the front end of the drill pipe; the rubber pipe is connected to the rear end of the drill pipe through the rotary water tail; the water pump is connected between the water tank and the rubber pipe and is used for supplying water into the drill pipe and the drill bit through the rubber pipe. The ultrahigh-pressure hydraulic device integrating drilling, reaming and cutting has the advantages that low-pressure drilling, medium-pressure reaming and high-pressure seam cutting are combined, drilling, reaming and seam cutting are integrated, coal free face is increased, coal internal fracture is increased, sufficient pressure relief and permeability increasing of coal are achieved, gas release difficulty is improved, the effective influence range of drilling is increased, gas extraction rate is increased evidently, extraction drilling construction quantity is reduced greatly, and the device is simple to operate, high in efficiency, evident in application effect and worthy of popularization and application.