Abstract: The nonlinear ground response considering the influence of pore water pressure is implemented by a new method. The cyclic mobility (CM) model, an elastoplastic model with rotation hardening which can systematically describe the monotonic and cyclic mechanical behaviors of soils combining the subloading, normal and superloading yield surfaces, is employed in the nonlinear numerical analysis. Using the transform stress method, this model can uniquely describe the overall mechanical properties of soils under general stress states, without changing the values of parameters. Based on the CM model and two-phase field theory, an effective stress-based, fully coupled, explicit finite element-finite difference method (FE-FD) is established. The finite element method and explicit integration method are applied in spatial and temporal discretization, respectively. The multi-transmitting boundary is adopted on the artificial boundary. By introducing the Green-Naghdi rate tensor, the finite deformation analysis is presented. This method is strictly verified, and the calculated results of a real site are quite different among the authors', the equivalent linearization method and the normal nonlinear analysis method in one-phase media. The long-period value of ground response spectrum will be higher owing to sand liquefaction. Moreover, the liquefaction process of the saturated sand layer and its influence factors are also studied.