Abstract: At present, the design of the Building Information Modeling (BIM) for catenary cantilever assembly mainly adopts a universal installation model, which cannot accurately reflect the actual installation situation on site. This paper established a unit library to create a cantilever assembly template, and combined parameterized unit technology and custom entity technology to develop a BIM based catenary cantilever assemblydesign system. This system can quickly create and arrange a catenary cantilever assembly model, achieving automation and intelligence in assembly design. Practice has shown that the developed system has significantly improved the assembly quality and accuracy of the catenary cantilever model, which can meet the needs of the BIM design of the catenary and provide support for further promoting the digital and intelligent development of the catenary.