Passive zone improvement is one of the most effective measures to control the deformation of deep excavation in soft soil. However, the soil mechanical parameters of improvement zone often show strong spatial variability, leading to the uncertainty of overall deformation behavior of deep excavation. Therefore, a three-dimensional model simulating the process of excavation is built by FLAC^3D software, random field models for cement-soil parameters are established based on K-L transformation, then deterministic and probabilistic analyses are conducted. The maximum horizontal displacement of diagram wall and the maximum ground surface settlement in both deterministic and probabilistic analyses are compared. Distribution patterns for the two deformation indicators are fitted, and the influence of coefficient of variation in cement-soil properties on the effect for different passive zone improvement thicknesses is also investigated. The results indicate that:a critical improvement thickness exists while considering the spatial variability of cement-soil; the spatial variability of cement-soil has limited influence on the overall deformation behavior of deep excavation and needs no special consideration in holistic performance evaluation.