This project belongs to the field of civil construction. As urban development gradually shifts from an incremental model to an existing model, the renovation, expansion and functional improvement of a large number of existing building complexes have become an important part of urban renewal. How to realize the expansion and development of urban underground spaces under different restrictions, while maintaining the original style of existing buildings and ensuring the safety of urban operations, has become an important issue that needs to be solved urgently in urban renewal. This project conducts research on the technical problems faced by the underground space expansion of existing buildings in the city. In order to adapt to different situations such as the protection level requirements of existing buildings and the restrictions of the surrounding environment, it innovatively develops three technical systems: horizontal and reverse underground space development technology, long-distance displacement and reset connection technology of existing buildings, and in-situ reverse underground space expansion technology. Its main innovations are as follows: 1. Construction technology of underground space in existing urban buildings using horizontal and reverse methods. In view of the fact that the building complex can only be moved in a small range within the red line, the technology of adding underground space by horizontal pushing and reverse method was pioneered, the barrier-free construction technology of top-down roof was developed, and the technology of sliding and moving back to the upper plate of building bearings was developed. It has realized the full utilization of the planned land's horizontal and vertical space. The underground space has a depth of more than 25 meters, which saves more than 10% of the cost and shortens the construction period by 15% compared with the conventional method. 2. Existing building long-distance displacement and reset connection technology. In view of the fact that existing buildings allow large-scale displacement, the adaptive hydraulic balance displacement technology for existing buildings was proposed for the first time, the efficient and precise reset connection technology for existing buildings was developed, and the information technology for the entire process of displacement of existing buildings was developed. Guarantee technology has achieved safe displacement at the kilometer level, and the automatic control accuracy of the entire process reaches within plusmn;2 mm. 3. In-situ inverted underground space expansion technology for existing urban buildings. In view of the fact that the building complex is not allowed to move at all, innovatively developed a reverse active synchronous pile foundation underpinning technology, proposed a refined inspection technology for existing buildings, invented a non-destructive single-sided ductile reinforcement technology for century-old building masonry walls, and developed Underground space expansion, low clearance, zero-distance construction and groundwater control technology have achieved a technological breakthrough in the in-situ expansion of historical protected buildings to 5 floors underground. The project has obtained a total of 31 independent intellectual property rights, including 15 authorized invention patents, 11 utility models, 3 software copyrights, and 2 Shanghai City Construction Methods; 31 academic papers have been published, including 5 SCI/EI; 4 technical standards and 1 monograph have been compiled. The research results have been adopted by the industry standard "Technical Code for Reverse Construction Methods of Construction Engineering"(JGJ432 -2018), the Shanghai City Engineering Building Code "Technical Code for Reconstruction and Expansion of Existing Underground Buildings"(DG/TJ08 -2235-2017), the CECS group standard "Technical Code for Displacement, Tilt Correction and Addition of Floors"(CECS225 -2007), and "Technical Code for Underpinning of Buildings (Structures)"(CECS295 -2011). The project results have been included in the reconstruction and expansion project of No. 33 Bund Yuan in Shanghai, the reconstruction and expansion project of Hermes flagship store, the addition of a 5-story basement project of the Central Shopping Mall on Nanjing East Road, the overall displacement project of the protected building of the residential project of Plot 118 in Huangpu District, the Jiangsu Province Department of Finance The project to add an 8-story underground garage to the protected building, the translation project of Xuzhou Tongheyu Yinhao, the translation project of the former site of Wuhan Hanzheng Street Fire Protection Federation, and the translation project of the Xiawangdu Wang Mansion in Fenghua. It has been successfully applied in underground space expansion projects such as the Wenzhou Catholic Church underpinning and restoration project, with a total added output value of 530 million yuan in the past three years, providing a mature technical system that can be promoted and used for large-scale underground space expansion in urban renewal.