In view of mass computation of large-scale 3D scalar field correlation algorithm and slow data rendering, and on the basis of research and summary of key technologies of 3D scalar fields and volume rendering, the principle of volume rendering is discussed, focusing on the ray casting algorithm of volume rendering. The ray casting algorithm of volume rendering is improved with the parallel advantages of multi-node cluster. And by means of MPI parallel programming mode, the algorithm is run on the PC cluster environment and applied to 3D city modeling. It fully develops the high performance computing of cluster and greatly improves the rendering efficiency. The experimental results show that the algorithm makes good parallel efficiency and visual effects.