Abstract: An optimal irrigation and drainage non-linear programming model is proposed with the concepts of soil salinity threshold and critical underground water table,aimed at preventing soil salinization in irrigation district,furthermore,combined with the real conditions of Xinjiang Kongliu Unity irrigation district to approach the model.The solution of the model gives the optimal irrigation and drainage policies,regulation process of under-ground water table,variation process of soil salinity in the different crops planted area over a year,optimal leaching water over a growing season and preplanting leaching water for different crops aimed at preventing soil salinization for four typical years(P=20%、50%、75%、95%).