Abstract: Based on the characteristics of massive spatial data of 3D terrain in the ribbon corridor of the railway line engineering, this paper summarized the acquisition methods and data sources of the railway line engineering DEM(Digital Elevation Model), and studied the 3D terrain modeling methods and lightweight processing methods. The terrain of the test railway section was constructed by two modes of grid and triangle network respectively. Delaunay algorithm was selected to triangulate, and edge contraction and point deletion were used to lightweight the data.Experiments show that the Triangulated Irregular Network (TIN) model can reasonably express complex morphological surface with less data. Delaunay point-by-point insertion algorithm is more suitable for railway engineering three-dimensional terrain modeling. The methods of edge shrinkage and point deletion are used to lighten the data simplification. The comparison shows that the point deletion method is more effective, the main parameters have not changed and the distortion is less.