Neighborhood analysis calculation with 3×3 window is usually adopted to derive slope f rom Grid DEM.This method produces errors on the edge of terrain factors mat rix.This paper takes slope as an example , three areas with different terrain characteristics as test areas, studies the edge effect on deriving slope from DEM with different scale , analyses the relationship between the edge effect and DEM resolution, region area and terrain characters, puts forward some methods to solve or decrease impact of the edge effect .It is important for digitalterrain analysis with high precision. There are two indexes to express edge effect:the first is the change value of mean slope;the second is root mean square error on the edge when deriving slope. The result shows that, the change value of mean slope is related to DEM resolution,region area and terrain characteristics , RMSE on the edge when deriving slope is related to DEM resolution and terrain characteristics.