When the underground structures and buildings of rail transit do not match the renovation requirements, they should be expanded or even reconstructed. According to various reconstruction requirements, key technical difficulties in the design of the expansion and reconstruction of the existing metro entrance and exit are summarized. In this study, a case study is conducted on the reconstruction structure design of the entrance B of the Huangmugang station of the Shenzhen metro line 7. First, the overall construction of a sunken square is presented in terms of stationcity integration, fire protection design, operational organization, antiflooding capacity, landscape design, structural construction method, total duration, and investment of the transit oriented development(TOD) project. Then, the design of foundation pit support with the same depth of adjacent metro entrance, the existing station sidewall opening without reserved connection conditions, and the connection structure node of new and existing concrete are analyzed. The research results show the following: (1) Demonstration should be fully implemented before renovation, the structure and construction organization should be designed considering specific requirements, and antiflooding and emergency plan should be determined. (2) When constructing a foundation pit adjacent to the metro entrances and exits, the existing enclosure and reserve backpressure soil can be used to control the deformation of the entrances and exits and the surrounding buildings, and the structural deformation should be closely monitored, achieving informatized construction. (3) The floor unloading and sequential construction can be used to demolish the sidewall of the existing structure without reserved connection and temporary support conditions. Beam/column structures can be constructed to connect with the existing structure, and waterproof measures should be implemented.