Reasonable regulation of irrigation and drainage is an important way to decrease water resource waste and water pollution, and to ensure the sustainable utilization of water resources. In this study, appropriate irrigation and drainage methods are proposed by optimizing agricultural water and soil resources based on the current status of water resource utilization in irrigation district in Northwest China, and as much as possible to reduce the amount of irrigation and drainage while ensuring the necessary for salt leaching. A two-layer model was considered to maximize economic benefits and relative production through a nonlinear algorithm to optimize the crop acreage, irrigation quota and the amount of irrigation water at each crop growth stage. A support vector machine regression model for predicting drainage was constructed, including drainage and irrigation, precipitation, evaporation and groundwater depth. Additionally, the amount of drainage water was compared before and after the optimization of irrigation. The amount of irrigation water demand in a wet year (2014), normal year (2008) and dry year (2013) decreased by 23.85 million m(3), 12.85 million m(3) and 17.50 million m(3), respectively, after optimization of the crop planting structure and irrigation scheduling. Furthermore, the net economic benefit increased by 3.76 billion yuan, 1.14 billion yuan and 2.34 billion yuan, as compared with the actual output value. The amount of drainage water decreased by 8.60%, 8.93% and 5.21% compared to that with no optimization in a wet year (2014), normal year (2008) and dry year (2013), respectively. This method can scientifically allocate the amount of irrigation and drainage, feasibly improve economic benefits and prevent soil salinization, thus providing guidance for efficient water resource utilization and ecological protection in arid areas.
