Based on the South Extension Project of Changping Line of large-scale Metro, this paper aims at the problems encountered in the construction, such as high protection requirements for ancient buildings, large reconstruction volume, high technical difficulties and high environmental risks, etc. Through the establishment of building information modeling applications based on this project as a whole, as well as BIM foundation applications, such as: model and family database, three-dimensional technology, construction site layout, auxiliary schedule management, auxiliary safety and quality management and other applications, and creatively put forward the application methods based on the key and difficult points of the project. This method includes the comprehensive simulation analysis of BIM + Midas to guide the protection of ancient cultural relics, BIM-assisted 3D design and simulation calculation of special-shaped extension steel ring, shield disassembly and optimization process, BIM-assisted multi-point multi-professional cross operation, BIM assisted shield closely attached to the bridge pile crossing Xiaoyuehe River, and BIM assisted intelligent monitoring platform and other measures. Through the above measures to solve the major and difficult problems, it will provide guidance and reference for the application of BIM in large-scale subway construction and ancient building protection.