The fractal theory is adapted to resolve the simulation of irregular-shaped objects, however, the modeling technology is adapted to the modeling of regular-shaped objects. It can simulate the nature scenery to the life by combining the iteration function system（IFS）of fractal theory with the free surface modeling technology. With the application of iteration function system and the free surface modeling technology to computer aided design (CAD) environment and used the interface modeling Object ARX of CAD and Visual C++ to study the simulative algorithm of natural scenery. With the use of iteration function system to simulate the algorithms of 3D fractal plants. It applied the free surface (B-spline surface) to simulate a hillside. The practical application of a hillside and plants with fruit was given, it indicated that the simulative effect was natural and living.