A planar construction drawing is usually used to guide the construction of reinforced concrete structures in the construction industry. Due to a lack of effective technical methods, the accuracy of rebar engineering lofting is insufficient. The rejection rate of rebar is high, which results in high processing costs. Under the background of intelligent construction and BIM technology, the prefabricated factory adopts an automatic production mode to concentrate on steel bar processing, which improves production quality and processing efficiency and reduces production costs. Based on Revit secondary development, using the C# programming language, combined with the Revit API development interface, an automatic 3D modeling plugin for a reinforced concrete variable cross-section column is developed. The BIM model of steel bars is quickly generated, and the engineering quantity of steel bars is automatically calculated, which saves time for the designer to build the BIM model. It is conducive to the automatic assembly and intelligent construction of reinforced concrete engineering, which promotes the information and intelligent development of reinforced concrete structure construction.