The railway 3D visual design plays an important role in checking the rail projects and improving the quality of railway design, because the key to implement Railway a 3D visual design is to build a 3D model of railway line landscape. The study on the methods of building a 3D model of railway line landscape is of important academic significance and practical value. We constructed a 3D digital terrain model with aerial survey Data or manual survey data in the regional railway, utilizing plan, profile, cross section data and bridge, tunnel, railway bed data to create the 3D railway line model and merging the two models to form a 3D model of railway line landscape. Based on analyzing the algorithms of Delaunay triangulation creation in Domestic and abroad, in view of the situation of building DTM and the need of realizing railway 3D visual design, a divide and conquer algorithm of building DTM is presented. The algorithm uses square grids to manage disordered points, to form triangular meshes in grids, DTM can be obtained by merging the triangular meshes so that the work of sorting the disordered points before building DTM is reduced greatly; moreover, the algorithm utilizes sub area to control the vertices of convex hull so that the range can be predefined when searching support points, the workload of searching support points reduced and the speed of merging two triangulations raised. A method for inserting constrained boundaries in DTM based on the study of the generation of constrained Delaunay triangulation is presented. First, we searched for the diagonals not intersecting with the constrained boundaries. Then we used them to cut the influenced area. The method has the advantages of a plain principle and a fast speed. The method of utilizing plan, profile, cross section data and digital terrain model to establish the 3D model of the main construction of railway line and the terrain model is presented. It describes the irregular entity surfaces by cutting them into regular entity surfaces, so that it would be simple and raise for the drawing and display of the entities. The method does not only suit single track railway line but also the double track railway line. Merging terrain 3D model and railway line 3D model to build the 3D model of railway line landscape is the core of implementing railway 3D visual design. The key of merging the two models is to hide the ground where the railway line is to be constructed. The problem is studied and a divide and conquer method is presented. First, generating a regular quadrangular mesh by means of DEM data. Then finding the regions that railway bed is located and cutting the regions into grids. If the boundaries of a grid covers another grid, then delete the grid. If the grid contains the boundaries then forming two triangles using the four vertices of the grid. Finding out the points where the boundaries and the triangles intersect. Inserting the points and the vertices of the boundaries into the existing triangular mesh to form a new triangular mesh. At last deleting the triangles which is located in the boundaries and the ground is hided. Moreover, the problem of merging two railway beds which are interrelated and the terrain surface is solved by using the separate and intersect method and in the segment where the railway vary from a double track railway integral bed to two beds of single track railway or vice versa. Based on the mathematical model, the development of the railway 3D visual design system with object oriented programming is completed. The correctness is proved by using the software to make the 3D landscape model and animation of Xi′an Nanjing railway, Xi′an Yan′an railway and SuiLing ChongQing railway; in the meantime, the practicability and adaptability is discussed. The railway 3D visual design plays an important role in checking the rail projects and improving the quality of railway design, because the key to implement Railway a 3D visual design is to build a 3D model of railway line landscape. The study on the methods of building a 3D model of railway line landscape is of significant academic significance and practical value. We constructed a 3D digital terrain model with aerial survey Data or manual survey data in the regional railway, utilizing plan, profile, cross section data and bridge, tunnel, railway Based on the algorithm of Delaunay triangulation creation in Domestic and abroad, in view of the situation of building DTM and the need of realizing railway 3D visual design, a divide and conquer algorithm of building DTM is presented. The algorithm uses square grids to manage disordered points, to form triangular meshes in grids, DTM can be obtained by merging the triangular meshes so that the work of sorting the disordered points before building DTM is reduced greatly; moreover, the algorithm utilizes sub area to control the vertices of convex hull so that the range can be predefined when searching support points, the workload of searching support points reduced and the speed of merging two triangulations raised. A method of inserting constrained boundaries in DTM based on the study of the generation of constrained Delaunay triangulation is presented. First, we searched for the diagonals The method has utilizing advantages of a plain principle and a fast speed. The method of utilizing plan, profile, cross section data and digital terrain model to establishing the 3D model of the main construction of railway line and the terrain model is presented. It describes the irregular entity surfaces by cutting them into regular entity surfaces, so that it would be simple and raise for the drawing and display of the entities. The method does not only suit single track railway line but also the double track railway line. Merging terrain 3D model and railway line 3D model to build the 3D model of railway line landscape is the core ofposed railway 3D visual design. The key of merging the two models is to hide the ground where the railway line is to be constructed. The problem is studied and a divide and conquer method First, generating a regular quadrangular mesh by means of DEM data. Then finding the regions that railway bed is located and cutting the regions into grids. If the grid contains the boundaries then forming two triangles using the four vertices of the grid. Finding out the points where the boundaries and the triangles intersect. Inserting the points and the vertices of the boundaries into the existing triangular mesh to form a new triangular mesh. At last deleting the triangles which is located in the boundaries and the ground is hided. by, the problem of merging two railway beds which are interrelated and the terrain surface is solved by using the separate and intersect method and in the segment where the railway vary from a double track railway integral bed to two beds of single track railway or vice versa. Based on the mathematical model, the development of the railway 3D visual design system with object oriented programming is completed The correctness is proved by using the software to make the 3D landscape model and animation of Xi’an Nanjing railway, Xi’an Yan’an railway and SuiLing ChongQing railway; in the meantime, the practicability and adaptability is discussed.