Double dikes can be used to alleviate difficulties in river closure under high flow and big drop. Both dikes are required to share water drop during the closure process. However, in practice, it’s not easy to control the hydraulic conditions to obtain satisfactory results. A series of 3-D numerical experiments were conducted by CFD (Computational Fluid Dynamics) simulation on double-dike closure in simplified straight boundaries. The results demonstrated that two recirculation zones in reverse directions in the flow pattern, which were formed due to main stream diversion between the dikes, were necessary for the drop sharing of the downstream embankment. Through computational tests, the hydraulic diversion were found  to be capable of controlling this kind of stable flow pattern. The location and size of the diversion wall could influence the formation and stability of the flow pattern. In the presence of the two stable recirculations, the distance between two dikes had a minimum value for maintaining the recirculation but had less influences on the total drop and its allocation on the two embankments.