Abstract: This paper discusses the seriousness of bank erosion phenomena in the lower Yellow River,and evaluates some current numerical models for simulating the longitudinal and lateral deformations of riverbed.A conclusion is drawn that they are not applicable to simulate the full bed deformation process in the lower Yellow River Finally,a new 2-D composite model consisting of a 2-D-flow sediment mathematical submodel and a riverbank-erosion submodel is established.Through using all kinds of enhanced measures,this model can be used to simulatre both longitudinal and lateral deformations of riverbed in natural rivers,especially in the lower Yellow River.