A sunlit time computation model based on the DEM data in rough terrain is developed in this paper. In order to improve the accuracy of the calculation

an earth curvature adjusting factor Q is carried out in the model based on the former researchers. In this study

6 typical terrain areas within China were selected and their spatial distributions of sunlit time on the vernal and autumnal equinoxes

the Summer Solstice and midwinter day in two different resolutions （500m and 1km） were calculated using the developed model. The sunlit times calculated by the revised models were compared with the previous models. And the topographic and spatial-scaling effects on the sunlit time were analyzed through two aspects: the different terrain types and different spatial scales of the original DEM data. The changing rules of sunlit time according to the geomorphology and spatial scale were found out

which are very significative in applications.