Abstract: The Nianpanshan Complex on the Han River in Hubei Province is a Class II large (2) type project,which is a riverbed type power station。At present, the construction of the left auxiliary dam of the diversion channel and the sluice gate in the foundation pit has been basically completed, the power house and the navigation lock have not been completed. The temporary flood control standard for the dam body in flood period was designed to retain floods of 100 years recurrence period. When a flood occurs with a frequency of once every 10 years or more, the diversion channel and sluice gate jointly discharge the water.. Due to various reasons, it is difficult to remove all the cofferdams before the flood, resulting in the sluice gate not being able to fully discharge the flood according to its discharge capacity. Due to tight construction schedules，the complex flood conditions and working conditions，Physical model tests often cannot be simulated in time。In this paper, by using a planar two-dimensional flow mathematical model, the combined flow conditions of the sluice gate and the diversion channel are simulated in real-time and dynamically based on the construction progress, and a reasonable diversion ratio is obtained to provide technical support for safe flood management during construction.