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Earthquakes are likely to significantly affect the workability of subway tunnels by introducing severe damage or excessive deformation of the tunnel structure. In traditional approaches, the safety marginal is designed under some idealized assumptions. For example, in-situ soils are assumed to be uniform or layered, which may not always be the case in reality. In this study, the performance of a rectangular subway tunnel subjected to a far-field ground motion is numerically investigated using finite element method incorporated with random fields. The soil strata around the tunnel structure are modeled by a hysteresis-hyperbolic constitutive model, and the spatial randomness in the shear modulus of soil is considered by modeling the soil domain as a random field. The statistical parameters of the random field are considered to examine their effects on the seismic response of the soil-tunnel system. These findings may provide a useful reference for practical seismic design of tunnels installed in normally consolidated clays. Keywords: Tunnel, Seismic response, Shear strength, Spatial variability, Random fields