Nowadays, because of the severe contradiction between water supply and demand, a large amount of ecological water resources are occupied by other water-using sectors, resulting in the rapid degradation of the ecological environment, especially in arid and semi-arid areas of northwestern China. Therefore, in order to deal with the above problems, a multi-objective water resources optimization allocation model based on ecological water demand is established, which not only focuses on ecological water demand, but also can effectively deal with the conflict among multiple objectives. A case study was applied in Wuwei City, Gansu Province, China, which had maximum economic benefit and ecological benefit as objectives. A series of optimal water resources distribution schemes were obtained under different representative hydrological years. From the result, as representative hydrological years changed from wet to dry, economic benefit and ecological water deficit would vary from CNY [52.82, 36.32] x 108 and [2.69, 5.51] x 108 m3, respectively. It indicated that water resources have become one of the factors restricting the sustainable development of Wuwei City. Even when p = 25%, it still cannot meet the water demand. This indicates that Wuwei city needs to aggressively develop water-saving measures and new water resources in the future to deal with the acute water scarcity scenario. In addition, no matter what representative hydrological years are used, the results of the established multi-objective programming model are always in the middle of the results of the individual objective, indicating that the established multi-objective programming model has the advantage of dealing with water competing conflict among different objectives.