It has become a very common phenomenon that the influence of pit excavation to the adjacent environment， what corresponding measures should be taken in design and construction to ensure the safety of construction in process and existing has become a key part. This Paper analyses the influence of pit construction to adjacent tunnel by using the finite element software plaxis. The analysis results show that strengthening the palisade structure stiffness and partitioning symmetric excavation can significantly control the deformation of the existing tunnel. The design and construction of the engineering can ensure the safety of the existing tunnel compared with the conventional construction methods， and it also shows that preliminary analysis of influence to the adjacent underground building before pit excavation is very necessary.