Based on the analysis of the reconstruction process and corresponding problems of the old building, the paper discusses the BIM modeling process based on three-dimensional laser scanning technology, namely, acquiring the point cloud data of the existing building through 3D laser scanning, importing the point cloud processing software for preprocessing, and Revit software, docking establishes the process of building a BIM model of an existing building. Through the application of BIM technology in the pre-reformation, design process, performance design and other aspects of the existing building renovation design, it is demonstrated that BIM has a positive effect on the design and management of the existing building renovation design stage.