[Objective] Orthogonally stiffened plates with different plate-to-beam bending stiffness ratios are taken as the research objects to uncover the dynamic coupling characteristics of the beam and plate components of orthogonally stiffened plates, and reveal the mechanism and influence of dynamic coupling between the construction members on their intrinsic dynamic characteristics. [Method] The natural frequencies and mode shapes of numerical models under free boundary conditions and clamped boundary conditions are calculated using the finite element method. Through an analysis of variations in the natural frequencies and mode shapes of an orthogonally stiffened plate against the plate-to-beam bending stiffness ratio, the intrinsic dynamic characteristics of an orthogonally stiffened plate with different bending stiffness ratios are discussed, and the dynamic coupling characteristics between the beam and plate are analyzed. [Results] The numerical results show that with the variation of the plate-to-beam bending stiffness ratios, the dynamic behaviour of the orthogonally stiffened plate transforms between two kinds of characteristics: one dominated by the plate and the other one coupled by the beam and plate. The critical plate-to-beam bending stiffness ratios and the criterion for determining them are presented in this paper. [Conclusion] The dynamic coupling between the beam and plate changes the variation rate of the natural frequencies with the plate-to-beam bending stiffness ratio, leading to the dislocation and distortion of the mode shapes of orthogonally stiffened plates.