Interferometric Synthetic Aperture Radar (InSAR) is a powerful technique for precise topographic mapping. However, owing to the side-looking SAR imaging geometry, geometry distortions appear in mountainous scenarios. Because of phase discontinuities or the absence of a valid phase, it is difficult to recover accurate DEM in such areas with single-aspect InSAR data. Fusion of two or more different aspects of InSAR data can deal with this problem in practice. Experiments using two antiparallel aspects of airborne InSAR data are carried out based on this idea. To decrease the processing error in single-aspect data and fuse them seamlessly, a MOtion COmpensation (MOCO) method using iterative DEM is used to reduce the MOCO error. Besides, phase-unwrapping methods based on terrain characteristics are proposed to avoid phase-unwrapping error owing to phase discontinuities in areas of shadow and layover. Experimental results verify the effectiveness of the processing methods.