The invention discloses a method for estimating the storage capacity of a reservoir dam in a data-free area, belongs to the technical field of hydrology, and comprises the following steps: calculatinga confluence accumulation value of each grid unit above an outlet point by utilizing drainage basin DEM data; extracting riverway grids in the drainage basin; carrying out basin water body identification by utilizing basin remote sensing image data, and rasterizing a water body identification result; calculating the water body aggregation degree of the water body grids; calculating the water bodyreliability of the water body grids, and removing the water body grids of which the water body reliability is lower than a reliability threshold; selecting a plurality of water body grids as samples,and measuring or estimating the measurement water depth of the sample water body grids in the digital map; based on the measured water depth and the water body aggregation degree of the selected sample water body grids, establishing a relation curve of the water depth and the water body aggregation degree, and estimating the corresponding calculated water depth by water body grids; and carrying out water body division, and obtaining the storage amount of each hydraulic engineering according to the calculated water depth. The method is high in estimation efficiency, objective and reasonable inresult and beneficial to rapid estimation of the storage capacity of the reservoir dam in the data-free area.