The invention discloses an automatic water pesticide application device. A hull is divided into a power control cabinet, a pesticide liquid tank and an equipment cabin, and the hull is made of corrosion-resistant material and has long service life, high strength and acid and alkali resistance. An accumulator is used as the power of the hull, and a remote control, a receiving antenna and a receiving controller jointly control the running direction of the hull. A motor drives a drive shaft to move, the drive shaft drives propellers to move, the motor, the drive shaft and the propellers togetherconstitute a walking part of the hull, and the walking part of the hull adopts a two-propeller structure. High-concentration pesticide liquid dissolved or diluted in the pesticide liquid tank is controlled by a proportioning valve to be mixed in a certain proportion in a pipeline through a pesticide taking pipe and a clear water pipe, and the role of the proportioning valve is to adjust the proportion of the pesticide liquid and water. Mixed liquid in the pipeline is controlled by the remote control and the receiving controller to open and pressurize a pharmaceutical pump, and the high-pressure pesticide liquid is delivered to a fan nozzle located on the tail portion of the hull to achieve uniform spraying of the pesticide liquid.