Abstract: Some reservoirs in China have no storage capacity curve or the reservoir storage capacity curve is outdated, which can not truly reflect the actual storage capacity. In order to accurately and efficiently master the reservoir capacity curve, taking Wangjiawan Reservoir as an example, based on the multi-temporal polarimetric SAR (Synthetic Aperture Radar) image data, the area of the reservoir water area is extracted using the multi component scattering model (MCSM) decomposition method, and then combined with observation data of the reservoir water level, the functional relationship between water level and area is fitted, and the reservoir capacity curve is deduced using the calculus principle, and the accuracy of the reservoir capacity curve is further confirmed by the water balance method. The results show that the difference between the calculated value of storage capacity increase by the water balance method and the calculated value of storage capacity increase by the storage capacity function and the storage capacity curve is very small, which proves the correctness of the storage capacity function and the storage capacity curve. The research in this paper shows that the method of drawing reservoir capacity curve using polarimetric SAR image can significantly improve the drawing efficiency and save a lot of manpower, material and financial resources on the premise of ensuring the accuracy of reservoir capacity.