Reinforcing structure and method for shield tunnel underneath passing existing building group

The invention relates to a tunnel construction reinforcing technology, and particularly discloses a reinforcing structure and method for a shield tunnel underneath passing existing building group, the reinforcing structure comprises a building reinforcing foundation and a tunnel reinforcing body, the building reinforcing foundation is located on the lower portion of a foundation of a ground building and used for supporting and reinforcing the ground building, and the tunnel reinforcing body is located on the upper portion of the tunnel. The building reinforcement foundation comprises an enlarged foundation precast slab and anchoring bodies symmetrically arranged on the two sides of the enlarged foundation precast slab, a pouring pipe is arranged in the enlarged foundation precast slab, and a grouting branch pipe penetrating into a soil layer around the enlarged foundation precast slab is further arranged outside a pipe body of the pouring pipe; a containing groove is formed in the top of the expanded foundati