Abstract: The regional water resources complex system develops with S-type pattern,so the process can be described with Logistic curve(L-curve) and Gompertz curve(G-curve).The analysis of differential eguations shows that the growth period and the golden period of L-curve,and the growth-period,the golden-period and the autumn-period of G-curve are the sustainable development period.The analysis of diffefence equation of L-curve shows that the development speed is the key factor for the sustainable water resources utilization Lower speed will obstruct the society development,and higher speed can lead to the unsustainable development Furthermore,the process of the sustainable development can be described with combined S-type curve,which contains the start period,growth period and golden period of L-curve and G-curve.At the end,a fitting is made with an example,and the result shows that the development processes of Dalian water resources complex system and Yantai water resources complex system from 1996 to 2005 are both the combined L-curve with two layers.