Abstract: Based on estimating rule of the normal vector angles between two adjacent terrain units,we use the conception of Terrain Complexity Factor to quantify the terrain complexity of DEM,and then the formula of Terrain Complexity Factor in Raster DEM and TIN DEM has been deduced theoretically.In order to make clear how the Terrain Complexity Factor h-and the Average Elevation RMSEEt affect the accuracy of DEM Terrain Representation RMSEEt,the formula of Gauss Synthetical Surface has been hired to simulate several real terrain surfaces,each of which has different terrain complexity.Through the statistical analysis method of linear regression in simulation data,the linear equation between Accuracy of DEM Terrain Representation RMSEEt,Terrain Complexity Factor ECF and the Average Elevation h-has been achieved.We provide a new method to estimate the accuracy of DEM Terrain Representation RMSEEt with a certain terrain complexity,and also will supply convincing theoretical evidence for DEM production and the corresponding error research in the future.