The present paper discusses agricultural water supply in the plain downstream of the Ha-ihe Basin, where water is unsatisfied with water demand. On the basis of water saving policy concerned with water development and management, the concept of an analytical model for decision making is suggested in this paper. The model can be used for either large area or small area. In this paper a large plain area of the Haihe Basin is taken as a case study.The mathematical model is obtained as follows: Where: Z = total profit (value of the objective function);B=benefits of water use;C = costs of water supply; = management level at e;I = water duty; A = irrigation acreage to be developed by using different flooding technigues, subscript of i;n = farming structure (cropping system);m = source of water (water supply combination);P = reliability of water supply. In this study, n and m are constants.There are many constraints involved in the model such as water amount, irrigation acreage, irrigation technique etc.The results show that water saving would be of the most important alternative to solve the problem of water shortage in the Haihe Plain. The net benefit of water supply through water saving techniques can be positive in a dry year. Enhancing the irrigation management should be emphasized on water saving. On the basis of water saving agricultural water resources can be supplemented through water diversion from the Changjiang (Yangtze River) to the Haihe Plain with a reasonable scale. Before the implementation of the water diversion a countermeasure of adjusting the cropping system of the Haihe Plain to mitigate water shortage is likely to be advisable.