Interferometric Synthetic Aperture Radar is one of the most important technologies for topographic mapping. The DEM quality of airborne InSAR system depends on both system hardware performance and data processing methods. To derive large scale topographic and thematic maps up to scale 1:50000 and 1:10000, the whole data processing methods were presented. The methods included SAR imaging, interferometric processing and cartographic processing. Special methods were induced to resolve the problems encountered in project applications. Results using X-band airborne InSAR system data showed validity of the algorithm.