Abstract: The geometric rectification method based on SAR image simulation, with advantages of no requirement to the ground control points (GCP) and precise imaging parameters and of that all the processing can be done automatically, has been gotten broad attention and used widely. However, the input parameters of SAR image simulation (such as the course angle, flying height, near slant range, digital elevation model data, etc) bear errors since the measuring equipments are imprecise. This will change the feature of the simulated SAR image, and cause the error of the image matching parameter (such as GCP precision) at worst, and then reduce the geometric correction precision. This paper analyzed the influence of the input parameters and GCP in the SAR image simulation and image matching. Furthermore, the error impaction of parameters was analyzed completely, and the corresponding calculation formula was also derived. The vacancy left over in current papers has been filled.