Abstract: In order to study the stability of branch channels o f Yangtze River's middle and lower reaches ,on the base of summarizing the evolu tion features of branch channels,the causes of longterm stability of branch ch annels are analyzed and explained by using automatic adjustment theory of riverb ed and energy loss minimum hypotheses.It is considered in this article that spec ific watersand conditions and control function of branch channel's import and export nodes make energy distribution to be achieved by transporting a specified discharge to branch.