The production of this product is based on the National Reservoir Mask Dataset (including a comprehensive geospatial dataset of nearly 100,000 reservoirs in China, Chunqiao Song, 2022) and the JRC-GSW Global Surface Water Dataset (Jean-Francois Pekel, 2016). It first overlays the two datasets to screen water pixels, thereby extracting reservoir inundation information, identifying target reservoirs and removing non-reservoir parts. Then, it analyzes the annual JRC surface water data to obtain the maximum and minimum areas of reservoirs as well as their inundation frequencies. The product production uses the National Reservoir Mask Data (a comprehensive geospatial dataset of nearly 100,000 reservoirs in China, Chunqiao Song, 2022) and the JRC-GSW Global Surface Water Dataset (Jean-Francois Pekel, 2016). By applying and overlaying the reservoir mask data on the JRC water body data, water body pixels within the mask range are screened to extract reservoir inundation scope and frequency information, identify reservoirs with seasonal variation characteristics and remove non-reservoir parts; then the JRC water body data of each year is analyzed to obtain reservoir water bodies, maximum and minimum water areas, and annual flooding frequency; finally, the annual water body frequency within the mask range is calculated, mathematical methods such as trend analysis are used to detect change points, thresholds are set to distinguish the nature of changes, and the year when the water body frequency significantly increases and then remains at a high level with small fluctuations is determined as the construction time of the reservoir.