Abstract: In order to solve the problems of water wastage, low utilization of surface water and over-exploitation of groundwater in Daman Irrigation District in the middle reaches of the Heihe River, the study predicted the water demand of the irrigation district in different planning years (2026 and 2030) according to the actual situation of the irrigation district using the grey prediction model with the water use quota method and put forward a multi-objective water resource allocation model including cost-effectiveness, water shortage risk and phosphorus pollution control, and adopted A-NSGA-Ⅲ (adaptive nondominated sorting genetic algorithm Ⅲ) algorithm to solve the model and establish an evaluation system of water resource allocation schemes. algorithm to solve the model, establish an evaluation system of water resources allocation schemes, and optimize different allocation schemes by CRITIC (criteria importance through intercriteria correlation) - TOPSIS (technique for order preference by similarity to an ideal solution) method. The results show that: the planned water delivery metric of Daman Irrigation District in 2026 and 2030 are about 13839700 m³ and 3329300 m³ short of the predicted maximum water demand, of which 26662800 m³ and 2633900 m³ are short of surface water, respectively, and the groundwater can satisfy the demand in 2026, and there is a shortfall of 695400 m³ in 2030, which is a prominent contradiction between the water supply and demand; after the optimal allocation, an evaluation system of different water resources allocation schemes is established, and the different allocation schemes are preferred by CRITIC-TOPSIS method. The contradiction between supply and demand is prominent; after optimized allocation, the total water consumption of the irrigation area in 2026 is 210430000 m³, of which 146740000 m³ is used for surface water, 636900 m³ is used for groundwater, and 100000 m³ is left over; in 2030, the total water consumption of the irrigation area is 214591700 m³, of which 164456400 m³ is used for surface water, 50135300 m³ is used for groundwater, and the remaining water is 6018300 m³. The two programs meet the constraints of the total annual water supply index of the irrigation planning. In 2021, the total water resources used in Daman Irrigation District will be 241725300 m³, of which the surface water use will be 115020500 m³, and the groundwater use will be 126704800 m³. Compared with the year 2021, the surface water use in different planning years of the allocation program will increase by about 31719500 and 49435900 m³, respectively, and the amount of groundwater exploitation will decrease by about 63014800 and 76569500 m³, and the proportion of groundwater use is reduced by 22.15 % and 29.06 %, respectively, which reduces the exploitation of groundwater in the irrigation area to a larger extent. The multi-objective water resources optimization model proposed in this study has good feasibility and applicability in Daman irrigation district, and the water resources optimization scheme is in line with the reality, which can provide theoretical support and reference basis for water resources optimization in other irrigation areas in the middle reaches of Heihe River.