Abstract: Objectives Ships are subjected to dynamic loads caused by waves and slamming during actual sailing. When the load on the hull structure exceeds its load capacity, accidents will occur. Therefore, it is of great significance to evaluate the dynamic ultimate strength of ship structure. Methods Smith method has been widely used as a method to calculate the static ultimate strength of hull girders. Considering the strain rate effect, inertia force and stress-strain relationship of stiffened plate elements under different strain rates, the dynamic Smith method is developed to calculate the dynamic ultimate strength of hull girders under constant velocity bending moment load. Results Taking the ship-size box girder as the verification object, the error of dynamic ultimate strength calculated by Smith method and finite element method is less than 10% at low and medium angular velocity. Conclusions The dynamic Smith method is a further extension of the traditional Smith method, and improves the calculation efficiency of the dynamic ultimate strength of the hull girder.