Abstract: The orthogonal stiffened plate is widely used in the field of marine engineering. Taking a simplified model of stiffened plates as the research target, and based on the Ritz method and the energy functional variation principle, the energy formulations of stiffened plates are deduced in this paper. For the orthogonal stiffened plate, two kinds of simplified methods (the orthotropic plate theory and the equivalent thickness method) are proposed. The analytical formulations of natural frequency of three stiffened plate models are discussed. It is observed that the analytical natural frequencies agree well with those from FEM results. Finally, the acoustic radiation characteristics of three stiffened plate models in the water, as well as in the air, are calculated. Overall, the proposed simplified method presents a new perspective for the vibration and low frequency acoustic radiation problem of orthogonal stiffened plates.