Abstract: In this paper,an improved two dimensional (2-D) numerical model for river flow,sediment transport and bank erosion is presented and applied to study the mechanism of channel pattern changes.The effect of secondary flow at river bends is taken into account in the 2-D model by adding a dispersion stressterm in the momentum conservation equation of river flow.The 2-D model simulations were compared with the laboratory experiments conducted in a curved flume,as well as with the field measurements from a long river section between Shashi and Shishou in the upper Jingjiang Reach of the Yangtze River.The laboratory comparison result reveals that the 2-D model in simulating the bank failure calculation is improved in comparison with other commonly used methods.The results also show that the 2-D model is able to simulate the field measurement.The imp roved 2-D model is relatively simple,easy to use,more reliable,and can be better to simulate fluvial processes in natural river channels compared to classical methods.