To research unsteady flow transition process in a single irrigation canal stretch for the purpose of ensuring the safe operation of irrigation canals and rational allocation of water, we consider adopting different operating modes, as well as different gate regulation modes etc., under the two operation conditions of constant upstream water depth and constant downstream water depth, conduct the canal unsteady flow numerical simulation with the rectangular grid characteristic method in the trapezoidal cross-section under the different gate controls, and compare the results of two operating modes and forecast time in advance to control the sluice at all levels. So, the results can fully reflect the dynamic and more precise adjustment process.