The invention discloses a high-speed train subgrade device by using water power. The high-speed train subgrade device by using the water power comprises a water power spray gun, an adjusting mechanismand a translation mechanism, wherein the water power spray gun is used for breaking a high-speed train subgrade by spraying a high-pressure water column, the adjusting mechanism is used for adjustinga breaking angle of the water power spray gun, and the translation mechanism moves along high-speed tracks; the adjusting mechanism comprises a advancing and retreating mechanism, an angle adjustingmechanism and a longitudinal movement mechanism, wherein the advancing and retreating mechanism is used for driving the water power spray gun to advance and retreat, the angle adjusting mechanism is used for adjusting the horizontal and vertical angles of the water power spray gun, and the longitudinal movement mechanism is used for adjusting a longitudinal position of the water power spray gun; and the translation mechanism is connected with the longitudinal movement mechanism through a cross beam. The high-speed train subgrade device has the advantages that manpower is saved, the subgrade breaking efficiency is high, the high-speed train subgrade is rapidly broken down, and the movement is convenient.