This study applied Biot's dynamic governing equations in Laplace domain and used the finite element theory to build the stiffness matrix of a porous medium 3D hexahedron element. Then, the matrices of porous medium 2D triangular element as well as quadrilateral element, porous beam, and porous plate 2D quadrilateral element derived by other researchers are adopted. Finally, the multipoint constraint approach is applied to generate the stiffness elements that related to the fluid displacements and complete the Finite Element Frequency Domain Analysis (FEFDA) of a stiffened porous plate coupled with a porous medium. This study used porous medium to simulate acoustic field and built a model of a stiffened porous plate coupled with an acoustic field. Based on the analysis results of the system of a stiffened plate coupled with an acoustic field, the FEFDA results of the porous beam, the porous plate, the stiffened porous plate, acoustic field, and the coupling of the stiffened porous plate and the acoustic field were verified. Then, through the geometric analysis and material parameter variance analysis, the influential factors of modal frequency and amplitude in the coupling structure were explored. According to the analysis results, besides the significant influence of boundary restraints on modal frequencies, the dynamic dissipation effects caused by the coupling of the fluid with the solid skeleton and the bulk modulus of the fluid were also the main factors influencing the system modal frequencies. In addition, the FEFDA of the stiffened porous plate coupled with the acoustic field conducted by this study could indeed achieve the goal of improving the acoustic behaviors of certain areas.