As a result of multiple factors, Scanned Images from papery topographic map will present the distorting errors. For the sake of rectifying the errors, the geometric rectification on scanned images is discussed. Based on the theory of finite element and the technology for image processing, the method of rectifying the distorting errors on the scanned image is presented. The method takes full advantage of reference points on the topographic map, and the region of map is partitioned into some quadrilateral elements by reference points, then bilinear equation is adopted to rectify the quadrilateral region one by one. The method not only makes the best of information of reference points, but also avoids operation of polynomial equation. Precision of rectifying the distorting errors on the scanned image is remarkably enhanced.