Abstract: The clipping process is realized in three steps. First, Cohen-Sutherland encoding is used to totally reject or accept line segments. Then, a new regular polyhedron with 12 square faces all inclined at 45° to horizontal plane and circumscribing the first clipping window is introduced. If a line segment is totally out of the box, it must be out of the window. The second encoding system is applied to reject more lines through projecting the new box and lines from 3D to 2D. Finally, the clipping process is completed by finding the intersection points of lines with window boundaries, the partition encoding is simplified through geometric transformation. Experimental results show that the new algorithm is robust and more efficient than classic ones.