A one-dimensional mathematical model for unsteady sediment transport in the Ningxia reach of the Yellow River was developed. In the model, the formulas for the sediment carrying capacity and the manning roughness coefficient, which reflect the features of the Yellow River, were adopted. A coefficient of sediment distribution was defined to represent the ratio of the bottom to the average concentration under the equilibrium conditions, which is not constant 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 were also estimated in this model. A four-point (Preismann type) finite difference scheme and TDMA were employed in the numerical simulation. The amount of sediment deposition during the period of 1993～1999 in the Ningxia reach of the Yellow River from Xiaheyan to Shizuishan with a length of 197.43km were numerically simulated with the model. The computed results, such as the amount of sediment deposition and water stage agree well with the field data. Finally the validated model was used to predict the riverbed deformation during the period of 1999～2019 in the Ningxia reach of the Yellow River.