A2-D depth-average far-field numerical model that can be applied to simulate the jet pollution into natural river has been made in the paper.The theory of Large Scale Turbulent Simulation to natural river has been adopted in the model.It also used the upwind scheme of Peaceman-Rachford's alternating scheme and Douglas alternating scheme in the diffusion process.The model has also been successfully applied to the jet pollution calculation of some large,middle and small rivers in China.