The finite element model of support structure gridding underground diaphragm wall of a deep foundation pit in Nanjing is established; and MohrCoulomb elastoplastic constitutive model is adopted for rocks and soils. The finite element method is used to analyze the deformation of the deep foundation pit and the distribution rules of soil stress; and the results are compared with measured data and Rankine soil stress. The influencing factors, i.e. depth of backwall and separating wall, width of backwall, thickness of frontwall and foundation reinforcement, are analyzed. The analytical results show that: 1) The lateral deformation of gridding underground diaphragm wall is similar to that of cantilever beam. 2) The lateral deformation of wall roof is the largest, which shows that the deformation rules of the abovementioned underground diaphragm wall are different from that of conventional multiplesupported structure. 3) The influencing factors of thickness of frontwall and reinforcement of foundation pit are obvious.