Reconstruction of old buildings has emerged since the 21st century. Traditional construction method has many defects such as lack of digitalization technology and informatization management, poor cooperativeness and incapability of evaluating the efficacy of building reconstruction. How to systemize the reformation design of old buildings is focused. In this study, building information modeling (BIM) was applied in the reformation design of old building structure, and the performance was simulated and analyzed. Moreover, it was applied in practical construction. An old building in Guangdong was divided into two areas and a courtyard using BIM. Relevant reformation countermeasures were put forward to solve the problems of the building. Then simulation analysis was performed. The results demonstrated that BIM could be applied in the reconstruction of old buildings. The application of BIM in reformation of old buildings can make up the deficiencies of the traditional design methods and make the design more intuitive.