Abstract: A one-dimensional mathematical model for unsteady sediment transport in the lower Yellow River is developed In the model,the formulas of sediment carrying capacity and Manning roughness coefficient,which can reflect the features of two-phase flows in the Yellow River,are adopted.A saturation recovery coefficient is defined to represent the ratio between the bottom and the average concentration under the balance conditions,which is not a constant in this model and is evaluated by using an empirical expression obtained by integrating the sediment concentration along water depth.The concentration distributions and the mean diameter distributions of suspended sediment in the transversal direction are also est imated in this model.The Preissmann four point infinite difference scheme and algorithm for Tridiagonal Matrix Eqs.are employed in the numerical method.