Abstract: This paper presents a formula regarding the relationship between spatial resolution of RS image and mapping scale on a study area. The common high resolution RS images, choosing IKONOS and QUICKBIRD as the models in this study, are rectified by certain scale relief map related. Then some reference points in the study area were measured by RTK GPS to get some base points as true value. The difference between the value on the RS image and the RTK GPS value can be used to work out a geometry revised coefficient, divided by the resolution of RS image, which can be used to figure out the mapping scale.