Abstract: Objective To analyse morbidity of dental fluorosis after 30 yrs of defluoridation water improvement in Xiangshan peninsula, and to predict the prevalence of dental fluorosis in future 5 yrs. Methods Data on defluoridation water improvement in Xiangshan peninsula during 1982~2012 was collected, and rank correlation analysis used to explore the relationship between prevalence and time. The ARIMA model analysis in time sequence was used for building model and predicting the prevalence of dental flusosis. Results The prevalence of dental fluorosis before defluoridation water improvement was 76.36%, and 10 yrs, 20 yrs and 30 yrs after were 46.20%, 0.98% and 0.35% respectively. The difference between them was significant and showed by χ² test (χ²=107.71, P<0.01).The rank correlation analysis showed that the prevalence rate was decreased with time (r_s=0.99,P<0.01). The prevalence of dental fluorosis in the future 5 yrs would be 0.29%,0.20%,0.15%,0.12%,and 0.10% as was predicted by ARIMA model. Conclusion The prevalence of dental fluorosis has been decreased year by year, indicating that the defluoridation water improvement has been effective.