In this paper, the SPH method is modified by incorporating a new coupled dynamic solid boundary with high calculation accuracy, in which non-penetrating condition is maintained within the particles and the free surface conditions are applied by using the sum of the support regions of corresponding particles. This method is expected to provide an accurate estimation of the rolling and broken effects of the water flow. A simplified flooding flow model is thus established to examine the effect of bulwark against the flood, in which various characteristics of the 3D flooding flow are well predicted. The collapse behavior of the cylindrical body of water is simulated using a 3D SPH model. The finding shows that the numerical results agree well with the experimental results, which demonstrates the effectiveness of the modified SPH method in modelling the free surface with violent flow behavior.