The spillway is one of the most important construction components in the irrigation system; it is the key to ensuring the safety of the reservoir. In this study, the 3D-Fluent numerical model is used to simulate the hydraulic regime in the Ta Hoet spillway. The 8 simulation cases include different gate opening modes and variable flood flows. The change in velocity, water surface, and other hydraulic factors on the spillway have been studied in detail. The results also show that the direction of flow into the spillway is not straight but curved, resulting in different hydraulic regimes at the valve gates. The model results have been calibrated and show excellent accuracy when compared to the experimental data