RevitAPI is one of Revit's secondary development tools. In this paper, the application of RevitAPI and the main process of secondary development of Revit are introduced. An assistant modeling software for architectural fire sprinkler is developed by C# and Visual Studio2010 based on Revit 2014. With this software, Revit in cooperative work becomes more efficiently and conveniently. Finally, practicable value of the software system is versified by engineering examples.