Abstract: Riprap breakwater has been widely used in port engineering. The model of riprap breakwater has been established by the two-dimensional particle flow method of discrete element methods, and the effect of two mesoscopic parameters including the stiffness and friction coefficient on model analysis has been analyzed. The parameters of the riprap breakwater particle flow model, which overcomes macro-continuity hypothesis in traditional continuum mechanics, have been determined by reasonably combining with engineering practice. Besides, the simulation analysis on the dynamic stability damage of the riprap breakwater has been made in a direct way. The research indicates that the weight of the breakwater is the main factor, which influences instability, and the second is the width of the levee crest and the grade of section. The overall stability of a riprap breakwater is better when the enrockment is heavier, the width of the levee crest is larger and the slope is slower. As for this project, structural improvement has been made for the riprap breakwater, and optimal submerged breakwater structures with different weight riprap and section shapes have been obtained by the application of this conclusion.