Abstract: The Sentinel-3 Satellite Synthetic Aperture Radar Altimeter (SRAL) data is one of the emerging data sources for monitoring water level. Based on the water body information of Poyang Lake extracted by Landsat-8 and Sentinel-2 optical remote images, the Sentinel-3A SRAL satellite measurements near Xingzi hydrological Station were extracted. According to the principle of satellite altimetry considering geophysical corrections, an outlier elimination rule and automatic calculation of each date satellite water level process were proposed, and measured water level was used to evaluate and calibrate the Sentinel-3A radar altimeter retrieved water level. Results show that the effective rate of Sentinel-3A satellite data in Poyang Lake is 64%, and valid data cover March to September. The Pearson correlation coefficient of satellite retrieved water level is greater than 0.99, and there is a significant correlation at the level of 0.001. The Pearson correlation coefficient between satellite water level change and measured water level change is 1, the average deviation is −0.175 m and STDEVA is 0.084. For ascending and descending orbits, the value of the statistics in descending orbit is better than those in ascending orbit. For high-water and low-water seasons, the values of the statistics in the low-water season are better than those in the high-water season, and the statistical index in the low-water season is the smallest: the average deviation is −0.082 m, RMSE is 0.107 m. The average absolute deviation of the calibration water level using the average deviation between the measured data and satellite altimeter water level in 2016-2017, 2016-2018, 2016-2018 as the calibration parameter both are 0.073 m, and R-value is 1. The water level calibration results based on different calibration parameters have little difference. The study has proved the effectiveness of the method of satellite altimetry data calculation and lake water level calibration, which is conducive to hydrology, climate change research, and monitoring of flood control and drought resistance.