Using the developed 1D and 2D flow mathematical models, the water - head distribution relationships between the upstream and downstream closure dikes were analyzed under the different gap widths of upstream and downstream closure dikes. Dike advancing sequences and corresponding closure riprap diameters for different closure discharges were proposed under the given water - head distribution relations. The calculated results of all kinds of closure projects also indicated that the risk of the closure dike advancing sequence is considerably high for the closure discharge of 12 200 m3/s, and it is very favorable for constructing for the closure discharge of 9 010 m3/s. The hydraulic conditions in the open channel during the real closure were calculated through using 1D and 2D flow models. The calculated results showed that the closure water - head was mainly shared by the upstream closure dike as its gap width was greater than 140 m or less than 50 m，and that it was shared by the upstream and lower dikes in this range. This simulated results agreed with the observed data