The invention provides a mechanical automatic water-jet cutting machine which comprises a main machine body, a supporting bottom face and a controller. The right side of the main machine body is connected with a transverse supporting plate and a water spray pipe, and the bottom end of the water spray pipe is connected with a sprayer. A water draining device and a supporting plate are fixed above the supporting bottom face, a water supply device is arranged in the main machine body, and the lower side of the water supply device is connected with a filter; the filter is connected with an energy accumulator through a connecting pipe, and the energy accumulator is connected with the controller through a connecting pipe. The controller is connected with an electronic valve and a hydraulic device through connecting pipes. The hydraulic device is connected with a supercharger through a connecting pipe, and the electronic valve is connected with the sprayer through a connecting pipe. Weighing sensors are arranged in the supporting plate, and a control unit is arranged in the controller. The mechanical automatic water-jet cutting machine has the following beneficial effects that full automatic control is adopted, materials are automatically sensed and cut and automatically machined, full automation without manual intervention is achieved, and high and precise production efficiency is achieved; moreover, human input is reduced for enterprises, and labor cost is greatly reduced.