Abstract: In this paper, the oharacterstics of environmental impact resulted from implementation of a water conservancy project is discussed, and the gradation structural system of regional environment impact factors is analysed by using the AHP method. For the complex conditions a method of quantitative avaluation of environmental impact is suggsted.As an example, the Nanyangqu water conservancy project in Gansu province is analyzed by this method, indicating the applicablity and effectiveness of the method.