In order to explore how to better apply the simultaneous localization and mapping (SLAM) 3-D laser scanning technology to the preservation of historical buildings and realize the purpose of digital preservation of historical buildings by using 3-D point cloud models, the historical buildings of the Bai ethnic group in Yunnan were taken as the research object, and SLAM 3-D laser scanning technology was used to obtain high-precision point cloud models of historical buildings. This technology can not only quickly complete the data collection work, improve the efficiency of the digital preservation of historical buildings, but also form rich digital achievements of historical buildings. Through the theoretical analysis and experimental verification of the experimental area data, the feasibility of SLAM 3-D laser scanning technology in the digital protection of historical buildings was proved. The results show that the error in distance is 0.004 m, and the error in point is 0.037 m and 0.021 m, and SLAM 3-D laser scanning technology can not only quickly and accurately complete the historical building data collection process and form a high-precision point cloud model, but also the flat vertical section extracted based on the model can meet the relevant specification accuracy requirements. This study provides a new idea and method for the digital preservation of historic buildings, which is expected to play a more active role in future applications.