The hydraulic automatic gate is a drainage device that utilizes the buoyancy of water to automatically open and close the gate. While ensuring a sufficient overflow height, the hydraulic automatic gate can effectively reduce the fixed weir height and width, reducing construction costs. It can maintain a constant water level in front of the gate and allow for emergency flood discharge without external power. At the same time, it effectively prevents suspended and floating debris from entering downstream. Leveraging its advantages, the hydraulic automatic gate is widely used in river outlets, flood storage reservoirs, flood pumping stations, initial rainwater storage tanks, and other locations.