Abstract: The length of re-circulation is an important index for design of spur dikes. Based on the data of flume tests and calculation results of mathematic models, the scouring processes of riverbed and the relationship between the relative length of re-circulation and the relative width of river are analyzed. The length of re-circulation decreases rapidly with the development of the scour hole, and the relative length of re-circulation decreases with the increase of the relative width of river.