It is very important to assess accurately geotechnical design parameters along the periphery of tunnel excavation. The geotechnical parameters most commonly used in numerical modeling for tunnel design are usually obtained by subsurface exploration and in-situ characterization before tunnel construction. These parameters generally indicate representative properties or the average values of the circumferential ground of tunnel in global scale. However, tunnel behavior during and after construction may be greatly affected by the spatial distribution of geotechnical parameters even in case that their average values are constant. The spatial variation of geotechnical parameters also may affect the long-term temporal response (e.g., creep) of tunnel behavior. Deformation characteristics of tunnel are apparently governed by anisotropic and spatially distributed geotechnical parameters rather than by isotropic and uniform geotechnical parameters. Thus, in this paper, a statistical approach on numerical modeling is suggested to explore the effect of spatial distribution in design parameters on tunnel deformation. A commercial program, FLAC2D, is used as a numerical analysis tool. As an input, normally distributed data sets were randomly generated based on statistical properties. The generated geotechnical design parameters were assigned to elements or/and zones. This process makes it possible to assess the spatial distribution effects on the deformation of tunnel. The site considered herein is a subway tunnel of Pusan, Republic of Korea, consisting of residual soil and soft rock. Various geotechnical parameters are investigated in view of tunnel deformation and their effects are quantitatively estimated in terms of an influencing distance from the outline of the tunnel. According to numerical analysis results, critical zones where the spatial distribution of design parameters affects the deformation behavior are clearly present, and the influencing distance from the tunnel is various with each geotechnical parameter. Finally, this paper presents what is the most sensitive geotechnical property, which should be investigated precisely, and the practical investigation distance from a tunnel.