According to the requirements of integral Stereolithography (integral SL) System, a new direct slicing method under Pro/ENGINEER environment is developed. 3D CAD models are sliced with Pro/TOOLKIT in Pro/ENGINEER environment, and section image of 3D models can be obtained and saved as image format. Dynamic masks are produced with the cross-section images which obtained through the slicing method by dynamic pattern generator, and then 3D real prototyping is fabricated conveniently with integral SL System. A 3D tower model is sliced with this method, and the tower prototyping also is fabricated with integral SL System. Compared with the STL format files slicing method, the new slicing method can achieve high accuracy of layer section profile. The direct slicing method provides a new solution for integral SL system to build objects with high accuracy.