Abstract: An improved two dimensional (2-D) numerical model for river flow,sediment transport and bank erosion is presented and tested in Part Ⅰ of this paper series.Using the 2-D model,a series of numerical experiments are further carried out in an idealized river channel with different variations of channel patterns in this study.The impact on channel pattern changes by various factors,such as initial channel slope,sediment supply,water discharge,and resistance to bank erosion is studied using the model simulations.The numerical results of river channel planform change,longitudinal bed profile,channel cross section,water surface profile and channel sediment transport are analyzed and discussed.The channel patterns simulated by the improved 2-D model agree well with the classic theory of channel pattern formation.