[Objectives] To analyze and optimize the crop planting structure in Ningxia based on the shortage of water resources and the large proportion of agricultural water consumption in Ningxia. [Methods] The change trend of crop planting area and planting structure in Ningxia in 2004-2018 was analyzed, and a multi-objective optimization model was constructed with the objectives of maximum crop profit and minimum water demand. The STEM method was applied to solve the problem, and the optimization scheme of crop planting in Ningxia was obtained. [Results] In Ningxia in 2004-2018, the planting area showed the characteristics of "increase-decrease-increase"; the area and proportion of cash crops were increasing, and the proportion of grain crops was gradually decreasing, but the proportion of crops with high water consumption was still high. After the planting structure was optimized, the economic benefit was increased by 34.85×108 yuan, and the water demand was reduced by 3.9×108 m³. [Conclusions] Under the premise of ensuring food security, the optimized scheme not only saves water resources but also obtains higher economic benefits. It provides a reference for alleviating water shortage and increasing farmers' income.