The invention discloses a high-pressure water descaling device for hot-rolled plate strip steel and belongs to the technical field of production of the hot-rolled plate strip steel. The device is characterized in that the inside of a descaling device box body is divided by three vertical separating plates and two horizontal separating plates inside the descaling device box body to form five water cavities communicating with one another, and the five water cavities include a water inlet cavity, a first water storage cavity, a second water storage cavity, a third water storage cavity and a water outlet cavity; a water spray gap is formed between corresponding positions of an arc-shaped surface of a nozzle moving plate and an arc-shaped surface of a nozzle fixed plate; the width of the water spray gap can be adjusted by the aid of an adjusting screw; and in the flow process of high-pressure water in the descaling device box body, the flow equalization effect can be realized under the effect of the separating plates, so that the descaling device has the advantages of being good in descaling uniformity and convenient to mount and clean.