Abstract: The paper introduces the bistatic SAR system of the TanDEM-X/TerraSAR-X, especially focusing on its flexible data acquisition model and the special advantages of a zero-time baseline. We present a bistatic InSAR processing method for DEM generation with TanDEM-X/TerraSAR-X data, highlighted by a phase difference strategy as a means of differencing bistatic interferograms and simulated phase from an external DEM, e.g. SRTM DEM. This strategy reduces the residual phase and improves the efficiency and the precision of phase unwrapping. We take account of the bistatic geometry and the corresponding zero Doppler time in SAR interferometric processing. The absolute phase offset was calibrated with some external ICESat points. A case study was carried out to generate the DEM product over the Puruogangri Ice Field in the Tibetan Plateau. Compared with the SRTM-X DEM and ICESat elevation, our preliminary results demonstrate the great potential of the TanDEM-X bistatic InSAR technology for mapping surface topography.