Abstract: Based on the observed data and the former research,the ergodic hypothesis is introduced to analyze the process of the reformation in the middle-lower Han river after the construction of Danjiangkou reservoir.It is concluded that the phenomena of replacement of spatial and temporal process is typical in the erosion development,the coarsen of riverbeds,the sediment concentration and the change of river regime,etc.The phenomena originate from the same response to the same generation in the self organized process of rivers in the process.Change of flow and sediment conditions,inflow of branches,the different river boundary conditions and the different respond methods caused by the different of river boundary conditions are the cause of complex response in replacement of the spatial and temporal process.The proper numerical method of replacement of spatial and temporal may be useful to the rivers downstream of many reservoirs.