Abstract: Objective：To observe the changes in enamel of rat incisor under chronic fluorine poisoning，and establish a new index for evaluation of dental fluorosis in rat. Methods：20 Wistar rats were randomly divided into four groups by gender. Control groups were divided into male and female group, fed with double-distilled water. Fluorosis groups were fed with double-distilled water containing 100 mg/L of F﹣ for 8 weeks. Under natural light, the changes of the mandibular incisor enamel were recorded by digital camera. The progress of dental fluorosis was evaluated by an improved dental fluorosis index. Results：Compared with control group, the enamel of dental fluorosis changed in different degrees, such as clarity, glossiness, surface defects. The progress of dental fluorosis had a significantly increased by drinking fluoride time. Under the same condition, dental fluorosis index of the different genders had no significant difference in sex（P > 0.05）. Conclusions： The improved dental fluorosis index can be used to evaluate the severity of dental fluorosis in rats objectively.