Abstract: SLGRAPH, a 3D data visualization system on geological application is introduced in the paper. Its design technology incorporates both ideas of object orientation and problem orientation, which gives the system a higher dynamic extensibility and reusability of codes. SLGRAPH has well considered the dimensional continuity of stratum and fault, modeling them in views of 3D. Supported by the technology of dividing spatial cells and encoding by their regions, it figures the discrete 3D data field quite accurately and solves the problem of fault. Then, improvement of the algorithm of removing hidden lines by floating horizontal line and rendering by ray trace are presented.