Abstract: The Nanjing Deji Plaza(Phase 2)project is located at the center of Nanjing. Excavation depths of main building and attached building are 21.50m and 19.70m respectively. The excavation depth of the foundation pit is deep. The pit area is huge. This paper analyzes the project structure, engineering geological conditions, hydrogeology conditions, surrounding environment and especially protection of subway tunnel. Pit support structure adopts underground diaphragm wall with two walls joining together. The attached building is constructed with top-down method. The main building is constructed with down-top method. This paper has put forward the protection measures to subway tunnel. In addition, this paper uses the general finite element analysis software to calculate the influence to subway tunnel by foundation pit excavation. The results show that this project has little impact on surrounding environment using top-down method, and meets the requirement of tunnel deformation with metro operation. This paper has a certain guiding significance for the projects with top-down method.