| Water resources are the material basis of human survival and development and important guarantee of sustainable development. Optimal allocation of water resource is the important content of sustainable utilization and optimal management, which determined the sustainable development of social economy and environment, and is also the effective means for improving the efficiency of water resource and solving the water shortage. So, study on the optimal allocation of water resources is an important theoretical value and practical significance and it is particularly essential to strengthen the new theory and new method.With the development of society and economy, water resources has become increasingly shortage and the conflict between water supply and requirement is aggravating in irrigation area, so, how to optimizing dispose the limited water resource in irrigation area has became a research focus, and unified dispatching surface and underground water is a effective approach to solve the conflict. So, unified dispatching surface and underground water as the main purpose in this paper, and the optimization model about water delivery for crops and the combined operation model of surface and underground water were further researched. Study contents and research results including:(1) The water resources status in China was briefly introduced, the necessity to improve the management standard and utilization efficiency of water resources were discussed, the current research situation and developing trend at home and abroad was reviewed, and the research value and basic approach about surface and underground water union utilization was expounded.(2) The rainfall data of LaoRiver irrigation area from 1959 to 2002 was classified through system clustering method and the typical years (20%,50%, and 75%) were determination through fuzzy similarity priority ratio method. Agricultural irrigation water requirement was used to predict based on BP neural network..(3) The large scale system theory and insufficient irrigation theory were expounded, and the classification, virtues, defects and suitable condition about various water production functions were deeply analyzed.(4) The model of the optimal irrigation schedule of crop was established. The basic concepts and systems of optimal water distribution of crop were detailed discussion, and the two-level model based on the optimal irrigation schedule and optimal water distribution among the crops was proposed, which is according to the principle of insufficient irrigation and taking full advantage of precipitation, water saving and ensuring the crop high-yield. In addition, the irrigation volume during the growth period and the law of water consumption were set relation by constraints, which is realized the goal of maximal economic benefit and ensures the high-yield, so that, the maximum benefit was produced based on the limit water resource.(5) The model of surface and underground water union utilization was established, which is a spectrum structured progressive order model. The first layer of the model was the optimal irrigation schedule of crop that based on the insufficient irrigation, the optimization of irrigation schedule was based on the water production function. The second layer of the model is the optimal water distribution among the crops, the third layer of the model is optimal water resources allocation among the plots,the coordination of the models were solved by the benefit function of crop.(6) The solving method for the model of surface and underground water union utilization was studied. Hierarchical optimization method was used for three layers large-scale system decomposition-coordination model and the dynamic programming solving method was established, the iterative solution of the combined operation model was given.(7) Applying the model to water saving irrigation in LaoRiver area, the scheme of the integrated use of surface and underground water in 2020 was obtained.
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