The two-dimensional zero-inertia equations for basin irrigation were formulated as a standard scalar diffusion equation subject to Neumann boundary conditions. The formulation can handle anisotropic variations in hydraulic resistance. A numerical solution was developed using finite-volume method on unstructured triangular cells. The simulation performance of the constructed model was validated based on typical experimental data. The complete hydrodynamic model of basin irrigation was selected as the comparative model. The validated results show that the constructed model can successfully simulate the basin surface water flow when the basin surface microtopography condition is relatively smooth. Similar results were found in terms of both the water quantity conservation and convergence rate. Moreover, the computational efficiency of the constructed zero-inertia model is approximately 17 times of the complete hydrodynamic model of basin irrigation. Therefore, the constructed zero-inertia model has good simulation performance.