The kinematic wave model simplifies the equation of motion by stating that gravity head is balanced by friction head,which implies a uniform flow equation could be applied.By combining the continuity equation and the imposed initial and boundary conditions,the kinematic wave model can efficiently solve for the propagation of floods,debris flows,and warning waves,etc.using the method of characteristics.However,the method is usually applied to constant-width channels,which cannot reflect all practical cases.The purpose of this research is to extend the kinematic wave approach to channels of variable width.The research describes the distinctive wave motions produced in one-dimensional variable-width channels.Then we use changed variable method to simulate the flows in channels with variable section size and slope.Finally,we validate the proposed model and assess its efficiency by comparing the results with calculations from HLL Finite Volume numerical method and the historical data of the flood of the failure of Tangjiashan Lake.