A numerical model based on Lai's (1991) multimode scheme for fully coupled simulation of water and sediment movement in mobile-bed alluvial channels with nonuniform bed materials has been developed and tested. The original system of partial differential equations for water and sediment movement was first transformed into characteristic and corresponding compatibility equations. After some operations the characteristic equations rendered an eigenvalue problem, from which eigenvalues were obtained. Then, the transformed system was discretized in finite-difference form and solved by multimode scheme. Finally, simulated results demonstrated the potential capabilities and usefulness of the proposed model.