Abstract: Environmental Kuznets Curve is at present popular in the field of environmental economics. From the time when Grossman and Krueger used this conception, many regional data were analyzed with the method of regression analyses backed it up, but there are only a few theoretical data to testify the curve so far, so that it is hard to estimate when the turning point of environment quality will come. This paper established twoproducts model from the point of making the maximum social welfare. By using the index of consumption preference, the optimum environmental investment was then found and then the essential conditions for Environmental Kuznets Curve. At last conclusions were drawn in this paper. First, there are two turning points: one corresponding to the worst environmental quality,and the other with no pollutant damage beyond. Second, environmental quality is controlled by regional economic development, not only by economic growth, because all the parameters of nonenvironmental production function, pollutionemission function and pollutioncontrolling function are controlled not by economic growth, but by economic development. Therefore, in order to maximize social welfare, and to achieve earlier turning points, it is to important to adjust industry structure, to improve the policy of national income distribution, and to advocate rational consumption.

Key words: Environmental Kuznets Curve, environmental investment, consumption preference, turning point of environment quality