Abstract: The middle route project which transfers some water from the Danjiangkou Reservoir will decrease the streamflow of the Danjiangkou Reservoir, change the water balance and environment condition of the middle and lower basins of the Hanjiang River. It has an obvious effect on the economic and social development. According to the research on environmental water demand and economic and social water demand, combined with the gray connectedness and entropy, a water resource allocation model based on the theory of gray system theory is developed, providing the system analysis of water resource with a new method. The method is applied to optimally allocate water resource in the middle and lower basins of the Hanjiang River, and its feasibility is discussed with the satisfaction result obtained.

Key words: water resource allocation, the lowest environmental river water demand, gray entropy