Urban water is one of the important life-support systems to human beings. The regulation mechanism of urban water ecosystem is of great significance in maintaining the sustainable development of urban water resources and environment. Based on the synergism of five rules, discussions were carried out in this study to explore the regulation mechanism and model of urban water ecosystem. The results indicate that, the urban water "Six in One" principle possesses temporal and spatial, comprehensive and phrasal features.Gray evaluation model can quantitatively evaluate the health and sustainable degree of urban water ecosystem. The Six in One degree is positively proportional to the continuous improvement of urban water ecosystem structure and function. Finally, the comparative studies of some typical cases including Beijing Kunming Lake of Summer Palace, West Lake in Hangzhou, Nanjing Xuanwu Lake and Ji’nan Daming Lake were carried out to analyze the motivation of becoming well-known waters and then to provide references to urban water ecosystem construction.