Abstract: This paper presents an improved LOD algorithm based on ROAM. The improved algorithm brings out an thought of "first division then modeling", it first divides the large DEM data into some smaller sub-blocks and then establishes the real-time continuous LOD based on those sub-blocks according to the relationship between the viewpoint location and the space error. Last, this paper uses the improved algorthim to simulate the terrain of Jingjiang area and gets a good effect.