Steel portal frames have been widely designed and constructed in China since the end of the last century, and in recent years ERP management software systems have been used by more and more steel structure fabricators/constructors. This paper introduces the program principles and techniques of the development of integrated CAD software with ERP interface for the detailing design of steel portal frame structure, including the frame work, data structure, 3D modeling algorithm and automatic output of 2D drawings/ERP source data. In the system, steel members and connectors are modeled and visualized as 3D objects. All information, involving geometry, material, manufacturing, fabrication, installation, ERP data requirements and so on, are embedded in these 3D objects for the purpose of parametric modeling and subsequent data output. 3D solid model acts as the kernel of the system. Connectors of joints are classified and organized by way of logic hierarchy, 3D model of joint are assembled abide by the structural and geometric dependency relationship between connectors. The ERP data interface is embedded in the system. The raw data are directly extracted from the 3D model, then formatted and fed to certain ERP system.