The simulation of seismic wavefield at seafloor and ocean acoustic field, the influence of complex seabed media and seabed topography needs to be considered, involving the coupling between seawater, saturated seabed, elastic bedrock and structure. That means, we target simulation where several types of equations are involved such as fluid, solid and saturated porous media equation. The conventional method for this fluid-solid-saturated porous media interaction problem is to use exsisting solvers of different equations and coupling method, which needs data mapping, communication and coupling algorithm between different solvers. Here, we present an alternative method, in which the coulping between different solvers is avoided. In fact, when porosity equals to one and zero,the saturated porous media is reduced to fluid and solid respectively, so we can use the porous media equation to describe the ideal fluid and solid, and the coupling between porous media,solid and fluid turns to the coupling between porous media with different porosity. Based on this idea, firstly the Biot's equations are approximated by Galerkin scheme and the explicit lumped-mass FEM is chosen, that are well suited to parallel computation. Then considering the conditions of coupling on the irregular interface between porous media with different porosity,by solving the normal and tangential interface forces, the coupled algorithm is derived, which is proved to be suitable for the coupling between fluid,solid and saturated porous media. Thus, the coupling problem between fluid, solid and saturated porous media can be brought into a unified framework, in which only the solver of saturated porous media is used. The three-dimensional parallel code for this proposed method is programed. Considering the situation of sag terrain in water-bedrock, water-saturated seabed-bedrock system, the unified framework proposed in this paper is combined with the transmission boundary conditions to analyze the dynamic response of P wave incident, and the unified framework are verified by the results meeting the interface conditions.