The invention discloses a high-pressure water jet spraying device of a fully-mechanized excavating machine. The high-pressure water jet spraying device comprises a fixed plate, a fixed hole, a side hole, a water inlet, a connector, a connecting hole, a first connecting plate, a water cavity body, a baffle, a mounting box, a guide groove, a sliding groove, a push block, a sliding block, a groove, asecond connecting plate, a clamping hole, a movable cavity, a guide column, a spring, a clamping column, a round rod, a fastening bolt and a spray head. The bottom of the baffle is rotationally connected with the water cavity body, the push block can drive the clamping column to move leftwards while being pushed leftwards, then the second connecting plate on the baffle is rotated to the top end,the push block is released, the clamping column can be clamped in the clamping hole under the action of the spring, and the aim of preventing dust when the spray head stops working is achieved. Due tothe fact that the fixed plate is of a square structure, the connecting hole in the surface of the fixed plate and the connecting hole in the first connecting plate are located in the same position, the mounting angle of the high-pressure water jet spraying device can be adjusted by rotating the fixed plate, and the purpose that the mounting box is mounted upwards all the time can be achieved.