Because the construction of metro tunnel at shallow depth damages stratum, stratum stress is freed and corresponding deformation is generated, and then the nonlinear mechanical action's stress field and displacement field are studied. With the excavation of littoral tunneling at depth shallow, finite software is adopted to simulate the excavation of tunnel using partial excavation method. Taking Tianjin metro tunnel at depth shallow in inshore area soft weak surround rock for example, the mechanism of rectangular tunnel primary support large deformation process was studied. The law and extend of the influence of these factors on ground surface settlement are presented. The analyze results have showed that the excavating process is a non-liner irreversible process tightly related with in the tunnel surrounding rock and primary support stress and strain. Subsequently, corresponding technologic measures of how to control large deformation in stratum were proposed and fully applied to the construction of Yingkoudao metro station in phase I` project. Good effects were achieved in guiding tunnel construction.