Abstract: The ship motion calculation during the flooding process is primarily investigated in still water. However,the research is limited due to the lack of consideration of ship rolling. In this paper,the dynamic motion calculation model is established firstly. Then,based on time discretion,the numerical arithmetic algorithm is developed based on the fourth Runge-Kutta method. Finally,the proposed model is validated by experiment with three different flooding modes. The experiments reveal that the model and algorithm are both accurate and can be applied to simulate the ship rolling motion that serves as the basis of the ship stability calculation.