An integrated CAD / CAM software system of steel industrial plant structures is developed based on the BIM application. The system is composed of two seamlessly integrated modules: structure calculation module and post-process module, the interface between the modules is clear. And, the complexity of the software development is effectively reduced by this design patterns. Using object oriented programming technology, a series of intelligent solid classes are abstracted to describe parts with deferent geometric information, structure properties and design requirements in real structure. Objects which are instances of these hierarchical C++ classes and logical links between them were integrated into the AutoCAD drawing database to construct a three-dimensional model. Several key functions including parametric shortcut modeling, frames analysis and member checking, three-dimensional solid construction, node design and editing, and drawing generation are implemented. IFC interface and the interface with SAP, ETABS and MIDAS are also implemented.