The invention discloses a method for cutting a boulder in front of a tunnel by using high-pressure water. The method comprises the following steps that step one, first water isinjected into a water storage tank, then a base isplaced on a moving mechanism and sent into the tunnel; step two, then according to the environmental conditions in the tunnel, the height of a water cutting device is adjusted by a servo motor and a screw, and then the angle of a water cutting mechanism is adjusted by a telescopic cylinder and a connecting rod; andstep three, the water cutting mechanism is finally openedto cut the boulder in the tunnel. The free adjustment of the water cutting mechanism of the device isrealized through the arrangement of adjusting mechanisms, so that the efficiency of the cutting process of the device on the boulderisimproved, and the efficiency and safety of the tunnel construction areimproved.