Abstract: The evolution equations of river bends are proposed by using the self-organized theory and method which are the Fokker-Planck equation and the Langevin equation.And the qualitative achievements,such as the evolution laws of river bends, symmetry damaged, form transition, and developing trend,are got by detailed analysis of analytic solution of the Fokker-Planck and the Langevin equations and it's dynamic inferences.Finally, we analyze the evolution features of some really river bends.The theoretical results tally with the observed results.