The investigation of plants behavior under different flow conditions, because of the interaction between "depth and flow velocity " and also "the amount and type of plant bending and its rupture point", is a complicated phenomena. In this research, a dynamic analytical method is introduced to investigate the bending curve of flexible plants, maximum tensile stress, critical rupture condition and the rupture point in submerged condition. The results indicate that the rupture point locates near the base of flexible plants with uniform diameter, while it shifts upward for the others with a non-nuniform diameter. In this regard, the rupture point will move toward the water surface when the difference between the plant diameter at the top and bottom of which increases. Moreover, when plant's stem diameter increases, the plant experiences more drag force; that is, the amount of bending will increase when other factors remains fixed. Plants with non uniform diameter have larger deflection, and an increase in the plant flexibility will move the position of maximum deflection upward, which in turn influences the flow roughness. Additionally for flexible plants, dimensionless drag force decreases strongly with the increase of the Reynolds number; that can be translated as the presence of a less hydraulic resistance.