Give constrains of costs and technology in analysis, actual practice of 2D FEM is widely popular and demanded. In order to take advantage of 2D FEM to simulate 3D stress state, the concept of stress releasing ratio was generally introduced to represent the 3D constraint effect. For example, the simulation analysis of tunnel excavation is based on the measured actual deformation to provide stress releasing ratio, in the engi-neering of open excavation, the construction is, most of the case, targeted on alluvial de-posit with relatively soft stratum. However, the 2D FEM simulation lacks a clear and ra-tional basis in how to represent the effects of 3D constraint. Thus, in order to investigate the problem above, the author analyzed same engineering using both 2D and 3D individu-ally, and compared the corresponding results. Based on the 3D analysis, factors including the relationship between the model’s scope, stress releasing ratio, and construction condi-tion of 2D analysis were also examined.