Abstract: Aiming at the missing or imperfect functions in Civil 3D software′s pipe network module, the secondary development was carried out and several parametric modeling functions was added, so that the design of the drainage pipe network of municipal road by Civil 3D could be more efficient. Based on Civil 3D.NET API, a series of functions were developed by using C# programming language, such as parametric creation, batch modification, fast search and data conversion of drainage pipe network model in Civil 3D. On this basis, the main process and some technical details of the secondary development of Civil 3D pipe network module are discussed. Finally, through actual engineering cases, it was verified that the efficiency of pipe network modeling by Civil 3D was obviously improved by the secondary development.