Beach restoration projects often use vegetation to increase the shore stability. In order to study the influence of rigid vegetation on hydrodynamics and morphology，the cylinder is used instead of rigid vegetation to carry out a numerical simulation study of vegetation-flow-sediment under different vegetation densities，and the relationship of vegetation density with the velocity and bed shear stress is analyzed. The results shows that ：1）The numerical simulation flow velocity is consistent with experimental data. 2）With the increase of vegetation density，the velocity and bed shear stress increase first and then decrease.3）The bed morphology change law shows that the overall formation of sand ridge is not so obvious when the vegetation density increases to a certain degree，but appears as a local sand pile near the lower reaches of the single vegetation.