A simplified strategy and a segmentation algorithm to modify LOD for large-scale 3D riding scenes are presented. The simplified strategy based on the nodes of least square roughness is applied to simplify the complex meshes of scenes. The decreased accuracy of the error model and the variation of roughness values are solved by modifying Lindstrom algorithm and adding rules of simplification. Then the simplified model is segmented by the multi-channel cutting algorithm. The scene data resulted from the segmentation is judged by an evaluation system based on the error factors. Finally, the comparison with the traditional algorithm proves that the simplified strategy and the segmentation algorithm proposed by the paper are more effective to reduce the complexity of the large-scale 3D scene rendering and accelerate the real-time display of scenes.