Abstract: The Global Navigation Satellite System Reflectometry (GNSS-R) providess a novel solution for water level monitoring with high temporal-spatial resolution. It has a great potentiality especially in our country, in large and medium-sized dams or high-steep slopes of reservoir banks, which GNSS deformation monitoring systems have been established. It can provide abundant data resources without extra hardware equipment. In this paper, the algorithm of satellite reflection signal inversion of water surface height is deduced based on GPS signal-to-noise (SNR) ratio data firstly. And then available satellites and section are determined and the trend term removal and Lomb-Scargle spectrum analysis is completed on this basis to provide a complete data processing process of inversion of water surface height. Through the actual measurement at the dam body and the flood gate of Wohushan reservoir in Jinan, the inverted water level is compared to the actual measured water level. The results demonstrate that the accuracy of the inversion height of the two separate stations reaches the centimetre level and meets the water level monitoring requirements. It also fully verified the feasibility and reliability of GNSS-R water level monitoring using the established GNSS deformation monitoring system in the dam and reservoir area.