The paper simplifies the track-ground substructure model, then the three-dimensional wave filed Green’s functions of saturated soils are obtained by TLM. In order to overcome the limitation that TLM is only suitable for the problems of finite depth, a solution of paraxial approximation ,which can act as the underlayer boundary of TLM, is obtained by using a series expansion of the stiffness matrix of saturated half-space soil in wave-number domain. Moreover, a semi-analytical BEM is put forward, where the TLM fundamental solutions are employed as Green’s function of BEM and the corresponding computer program was established. Due to the saturated soil models, the effects of geometrical and material properties of the WIB were investigated and the results show that the isolation effect of WIB system in saturated ground is great under rail transit load. Increasing the shear modulus、thickness and width of WIB may improve the isolation effect, while only need small size in saturated soil.