To obtain dynamic real-time display of global topography data, based on the study of multiple LOD algorithms and synthesizing the advantages of three level-detailed algorithms, we propose an improved LOD algorithm based on extensible quadtree structure. Our algorithm adopts mipmapping method to simplify the grids, which keeps the efficiency of Ulrich and the simplicity of Geomipmapping. To eliminate the possible crack of different level-detailed blocks in splicing, we add skirt vertexed to the terrain blocks, so as to fully utilize the CPU batch in triangle processing and make optimization of the memory and speed. The experiments results show that the improved method can provide real-time and dynamic display of mass global topography data out of core. The combination with fractal algorithm has also increased the drawing resolution effectively.