The structure and working principle of the moving feeding device of the sand throwing fire extinguishing vehicle were introduced. The mobile feeding device was driven by three hydraulic cylinders. Under the control of the detection valve, control valve and reversing valve, the three cylinders can move in sequence or move together, and complete the working cycle. The mobile feeding device can be used as the bottom plate of the whole vehicle and the conveying device of materials, which has the advantages of large carrying capacity and a small footprint. The variation law of the output force and moving speed of the hydraulic cylinder was obtained by theoretical calculation and experimental test, which provides a basis for analyzing the power output and efficiency of the moving feeding device.