Abstract: In order to avoid that the quantity of irrigation water supply for food crops is zero, the minimum irrigated area or yield constraints for these crops are often added to a model of optimizing the allocation of irrigation water supply, and it significantly reduces the objectivity of the optimization model. Planting risk coefficient was introduced to the model of optimal allocation for irrigation water supply in this paper firstly. The model takes the maximum benefits for irrigation as the goal. An optimal allocation of irrigation water supply and irrigation area for different crops can be obtained by running the model, and the optimal allocation of irrigation water resources is realized using the crop water production function. The ratio of crop irrigation area to total irrigation area was calculated by using this model for Jiamakou irrigation district of Shanxi province, the results fitted well with the present ratio in the irrigation district. It shows that the model was reasonable and reliable, and could be used to guide the management of irrigation water in irrigation district. The results also have important reference values for guiding farmers to determine planting structure reasonably.

Key words: irrigation district, irrigation water supply, optimal allocation, risk coefficient, crop water production function