Abstract: In order to determine the water requirement, water requirement rule and rational irrigation quota in different stages during the growth period of alfalfa, the author used non- sufficient irrigation experiment, researched the water requirement rule and relationship of yield and irrigation quota and the rational irrigation quota of alfalfa in Xilin River Basin, and attained some experiment information about the water requirement of alfalfa under water-saving irrigation condition. It was showed that the peak of water demand for the first growth season of alfalfa appeared from the late June to early July, the maximal water demand strength could reach 5.09 mm/d; the water requirement of the second growth season of alfalfa appeared from the early August to middle August, the maximal water demand strength could reach 5.23 mm/d. The relationship between alfalfa yield and irrigation quota was considered as a quadratic parabola. To achieve the targets of maximum yield per unit area, irrigation production efficiency and irrigation production elasticity, and determine rational irrigation quota of alfalfa, this research could supply scientific basis for water saving irrigation program and irrigation forecasting.