In interferometric data coregistration, both the windows and polynomial approaches influence the offsets calculation and coregistration results because of the topography in the area of a SAR image. In this paper, by using precise orbit data of ERS satellite and topographic information, we analyze qualitatively the relation between offsets difference and several influence factors as elevation, distance from near range to far range and perpendicular baseline and the selection of the order of polynomial in different topographies. The results show the DEM influence in range direction has a direct ratio relation with the elevation and perpendicular baseline but an inverse ratio relation with the distance from near to far range, the DEM influence in azimuth direction has a direct ratio relation with the elevation but small correlation with the perpendicular baseline and the distance from near to far range. Moreover, in the polynomial approach different orders of the polynomial are needed in different topographies to achieve more accurate offset result.