The Area-Volume-Elevation (AVE) curve is the most important physical characteristic of a reservoir, which plays a key role in multiple purposes of reservoir operations (e.g., flood control, water supply, and storage monitoring). Here we present a method to derive the reservoir AVE curve using TanDEM-X data and test it over Lake Mead. First, the maximum water extent from 1984 to 2015 was used to extract the TanDEM-X data for the reservoir area. Then, the water indication mask (WAM) was applied to the extracted TanDEM-X data to obtain the valid values which were then used to derive the AVE curve. Validations against the lidar surveyed curve suggest high-accuracy Elevation-Area (E-A) relationship (with an R2 of 1.00 and an NRMSE of 2.19%) and Elevation-Volume (E-V) relationship (with an R2 of 1.0 and an NRMSE of 0.87%). This method can be extended to global reservoirs using the available DEM datasets, which will contribute to many aspects of geoscience studies and applications.