Abstract: Allocating water resources can greatly contribute to the safe and stable operation of irrigation canal systems in order to improve the management level. This study aims to predict the hydraulic transition of the unsteady flow in irrigation canal systems caused by gate regulation. There was a hydraulic response of canal sections under different flow control conditions. Taking a trapezoidal branched experimental canal as the research object, the Preissmann four-point implicit finite difference and the chasing methods were used to discretize and solve the Saint-Venant equations. A one-dimensional unsteady flow mathematical model was established for the open channels with complex internal boundaries using MATLAB programming language. 10 test working conditions were designed to verify the model accuracy. For instance, the different canal head flow rates and gate regulation modes were set on the branched canal for the original physical model. The water depth variation at 12 measuring points along the canal was obtained using an ultrasonic measurement. The spatial step size of the numerical model was determined to be 0.25 m after grid independence verification. Combined with the physical experiments and HEC-RAS software simulations, the accuracy and precision of the simulation model and solution were systematically verified from three dimensions: the stable along- the - way distribution of canal water levels after gate regulation, the time - series water level changes at each measuring point, and the dynamic process of water levels around Gate I. Multiple working condition was then simulated to verify the reliability of the model. There were quantitative mechanisms and systematic interaction between gate regulation parameters and hydraulic response indicators. Once the incoming flow at the canal head was stable, particularly for every 1cm increase in gate opening (corresponding to a 5% relative variation in opening), the descending rate of the water level in front of the gate increased by approximately 6%, the maximum water level drop increased by about 1.85cm, and the hydraulic response time prolonged by around 8%. Three parameters shared a significant positive correlation with the gate regulation amplitude. Although the maximum drop of the water level during regulation was related to the variation of the gate opening, the relative variation amplitude of the water level was outstandingly smaller than that of the opening. The water diversion was transmitted to raise the water level. A normal distribution was observed in the relationship between the water level variation amplitude and the water level rise stabilization time. An optimal regulation range was determined to minimize the canal water level fluctuation and the transition time. In addition, the water level at the canal outlet shared a trend of first rising and then falling when the gate opening increased. The optimal regulation range simultaneously enhanced the water level fluctuation and stabilization efficiency. Moreover, the diversion ratio was dominated by both the incoming flow and gate regulation. Especially under high-flow working conditions, there was a more significant intervention of gate regulation on the diversion ratio. The simulation model can provide rich data support for the gate group scheduling. Numerical simulation also shared the important practical value to explore the gate regulation on the water level amplitude and flow velocity. Effective scheduling strategies were formulated in the gate group. The finding can also provide the datasets and technical support on the joint scheduling of segmented gates.