Abstract: Objectives To study the dynamic characteristics of local structures in naval architecture and ocean engineering, the dynamic boundary equivalence method between truncated model and original model should be explored. Methods The finite element method is used to calculate the natural frequency and vibration mode of the V-shaped plate model and one-side elastic support under the free boundary. In addition, the natural frequency and vibration mode of the isolated plate model under the three-side free boundary are compared with the isolated plate model, and the equivalent law of the dynamic boundary of the truncated plate model is explored. Results The research shows that with the increase of the thickness of the attached plate, the half wave number m of the (m, n) order of V-shaped plates mode is constant along the coupled edge direction, and the half wave number n perpendicular to the coupled edge direction increases; With the increase of the length of the attached plate, the half wave number m of the (m, n) order of V-shaped plates mode is constant along the coupled edge direction, and the half wave number n perpendicular to the coupled edge direction of the attached plate decreases. When the coupling angle α between the main plate and the attached plate is between 40° and 90°, the attached plate of the V-shaped plate is equivalent to providing a fixed support boundary condition for the main plate.Conclusions A fast prediction method for the natural frequency corresponding to the partial modes of the V-shaped plate is proposed.