To study the role of riparian vegetation in the lateral migration of a riverbank and the effect of migration on the distribution of vegetation community, in-situ investigation and analysis of vegetation biomass in the slump blooks and vegetation diversity of the convex bank were carried out along the meanders of the Lanmucuo River in the source region of the Yellow River. A method for estimation of the migration rate of the riverbank was proposed. The results indicate that the migration rate is exponentially correlated with the vegetation biomass. Siltation of the convex bank under different recurrence floods formed five different vegetation bands corresponding to five typical vegetation communities. The lateral migration of the river has a moderating effect on the riparian vegetation ecosystem. A pasture regeneration mechanism was formed with a characteristic that the amount of pasture increased first and then decreased. The continuous primary vegetation succession played an important role in maintaining the long-term sustainable grazing function.