Abstract: Terrain model is a kind of important models,which can be widely used in the fields of aerospace,aviation and military,such as war field simulation,flight visulation,characteristics matching,special effects on movies and televisions,etc.Because terrain model contains large-scale data,it is very difficult to realize fast-speed rendering of terrain model.Some approaches have been put forward to solve this problem,for instance,mesh simplification based on vertices clustering,polygon simplication based on triangular collapse,and levels of details based on simplification,etc.Based on geometry simplification,these approaches are effective and can keep a good geometry topology,however,they lose visual characteristics.As a result,they often lower visual accuracy.So,it is necessary to find out a new approach to solve this problem. This paper gives a new approach to terrain model simplification and fast-speed rendering.Firstly,this paper analyses the data characteristics of terrain model,especially for digital elevation model(DEM),and points out that this kind of data has a large quantity of redundance.According to the principles of computer graphics,it is unnecessary to derive from all terrain data each time.Secondly,this paper gives two judging criteria of simplifying terrain model,and then,based on these criteria,gives an approach of viewpoint-based extracting field data and normal-based simplifying detail model.According to this approach,terrain scope is defined and a terrain mesh will be extracted from a large-scale terrain data,then,this terrain mesh will be repartitioned according to viewpoint and image mesh.The gained new terrain mesh with unequal intervals has been simplified relative to original terrain mesh.Because image mesh can express the highest accuracy of the current viewing,this mesh extracting can keep high visual accuracy and at the same time avoid the loss of essential mesh data.Afterwards,according to the second criterion given by this paper,the extracted terrain mesh data still has redundancy.In order to avoid this redundancy,this paper gives a new approach of simplification based on normal,which firstly computes the average normal of the point of intersection of the mesh.This simplification approach can keep most of details of terrain models.Thus,it is an effective approach. At last,this paper gives two groups of experiment results.The first group are the results of data extracting and mesh reconstruction,and the other are the results of the model simplification based on normal,which include two rendered images so as to be compared with each other.The experiment results illustrate that the new approach of simplification and fast-speed rendering for terrain model has the characteristics of large data compression ratio,fast rendering speed and high accuracy.