Abstract: Objectives In order to carry out numerical analysis and experimental test on dynamic performance of stiffened plates truncated from naval architecture and marine structures, it is necessary to address the issue of dynamic boundary equivalence to simulate the influence of the surrounding coupling structures on the dynamic characteristics of the truncated structure. Methods Finite element method is used to analyze the influence of coupling angle and length of the aligned plate on the free vibration behaviors of the V-shaped stiffened plate and the influence of elastic support stiffness on the free vibration behaviors of the orthogonally stiffened plate with one elastic supported edge and three free edges. A comparative study on vibration characteristics of the V-shaped stiffened plate with different coupling angles and different lengths of the aligned plate and those of the orthogonally stiffened plate with appropriate elastic support stiffness is performed to obtain a simulation method for dynamic boundary equivalence of the truncated stiffened plate. Results Results show that the sensitive range of the coupling angle of the V-shaped stiffened plate for the first four modes is 140° to 180°, and mode stability range of the length of the aligned plate is 0.6 m to 0.9 m. When the elastic support stiffness is small, the additional mass decreases the natural frequencies, increases the sensitive stiffness and narrows the frequency range of the sensitive stiffness of the orthogonally stiffened plate. When the elastic support stiffness is large, the additional mass has little effect on the natural frequencies of the orthogonally stiffened plate. The equivalent elastic support stiffness of the first four modes of the V-shaped stiffened plate decreases with the increase of the coupling angle. The variation of the length of the aligned plate of the V-shaped stiffened plate results in modal differentiation and mode shape distortion. Conclusions Despite of the difference between the mode shapes of the truncated stiffened plate and those of the orthogonally stiffened plate with elastic support boundary conditions in modal differentiation, the orthogonally stiffened plate with appropriate elastic support stiffness is qualified to simulate the dynamic coupling boundary conditions of the V-shaped stiffened plate.