Hydraulic structure or channel control of upstream and downstream stage difference is the decisive factor of water movement, is the most important factor in calculation of water discharge. In the plain, the stage difference is very small, so that the observation accuracy directly affects the accuracy of discharge lining and calculation, which cannot meet the social demand for fine distribution of water resources. In order to improve the measuring precision of stage difference, the river stage difference recorder was designed. The application of the recorder need not zero elevation correction and comparative stage observation. And at any quantitative level, the stage difference accuracy can be increased.