A map of coseismic displacement field can be drawn by interferometric processing of synthetic aperture radar (SAR) images taken before and after an earthquake. This differential interferometric SAR (INSAR) technique allows us to detect subtle changes in the surface of the Earth without any ground-based measurements in place before an earthquake. The resulting interferogram is a contour map of the component of the displacement in the slant range direction, that is from the ground to the antenna. Geometric distortions such as foreshortening, layover and shadow occur in SAR image, because SAR measures the distance between terrain features and the antenna. These limitations aside, it is required for repeat-pass interferometry that the SAR data must be acquired such that the speckle in the image pairs is correlated. In order to understand the observed interferogram, it is necessary to know the data acquisition geometry. We simulate the differential interferogram of the spaceborne SAR images using the location of antenna and theoretical ground deformation. We determine the orbit of the SAR satellite by piecewise polynomial interpolation and calculate the theoretical changes in range due to the earthquake using the elastic dislocation model. The slantrange-ward displacements predicted by these simulations help us to analyze and interpret observed interferograms. We apply this simulation to the 1995 Hyogoken-Nanbu earthquake to detect the effect of geometric distortion of the observed SAR images. The simulation shows the theoretical total displacement due to the earthquake is considerably larger than the slant-range-ward displacement. Geometric distortion due to topography is not so large in the surveyed area, because the range of the altitude is less than 800m. Although differential INSAR derives deformation map over periods of days to years with very high accuracy at any time, its potential applications, characteristics and technical limitations need to be more explored.