A numerical model of border irrigation flow is a useful tool in the design and evaluation of surface irrigation systems. A one-dimensional complete hydrodynamic numerical model of border irrigation was established by using the time–space hybrid numerical method. Differences in stability, convergence, precision, and efficiency of the one-dimensional model were analyzed and compared between the hybrid numerical method proposed here and the Roe finite-volume method. At the same time, the computational performance and simulation effects were validated based on the results of typical border irrigation tests. The results show that the hybrid numerical method provides better numerical stability and convergence with little water quantity-balance and average relative errors than does the Roe finite-volume method. The computational efficiency is about two times higher under the same measurement circumstances. The proposed model of border irrigation can increase computational stability and convergence, can improve computational precision and efficiency, and can provide a good numerical simulation tool for the design and evaluation of border irrigation systems.