The construction of water resources optimal allocation model is the premise and foundation of solving and evaluating the optimal allocation model of water resources. The allocation of water resources includes not only the simple allocation of water resources, but also the protection of water resources and the analysis of the relationship between water supply and demand. Aiming at the problem of water shortage in the receiving area of water diversion from Hanjiang River to Weihe River, the large-scale system decomposition and coordination algorithm is used to optimally allocate the water use departments of each district of the water diversion area from Han to Wei River in Shaanxi Province, and establish the water diversion project from Han to Wei River. Optimal allocation model of water resources in the water receiving area. The results show that: in the 2030 planning level, the water supply of key cities, Xixian new district, medium/small cities, and industrial parks were 153.57, 368.16, 632.04, and 208.68 million m3, respectively, and the corresponding water shortage rate was 2.8%, 5.6%, 8.4%, 11.2%. The water supply sequence has a lower water shortage rate than the previous one, and the water shortage rate of the domestic water sector in key cities is only 1.2%. From the water shortage situation of various water departments in 2030, it can basically meet the water shortage of water receiving objects and effectively improve the water shortage in water receiving areas.