Abstract: Objective To investigate the enamel demineralization in the application of orthodontic fixed appliance. Methods Select 78 cases adopted orthodontic fixed appliance in Department of Orthodontics in our hospital from June, 2010 to June, 2011. Analyze the overall condition of enamel demineralization and enamel demineralization (demineralized tooth number, demineralization rate, demineralization degree, demineralization index) in different tooth position after correction. And in the course of treatment, they were divided into one group ( no less than 3 times per day) and the other group (less than 3 times per day) according to the average frequency of tooth brushing to analyze the influence of toothbrushing frequency on soft scale index and demineralization index. Results ① In 1726 teeth from 78 cases, 54 cases (178 teeth) had enamel demineralization. The incidence rate and demineralization rate were 69.2% and 10.3% respectively. The average demineralization index was 0.032±0.029.② Among the 1726 teeth, 1548 teeth (89.7%) belonged to demineralization degree zero; 111 teeth (6.4%) belonged to demineralization degree I; 59 teeth (3.4%) belonged to demineralization degree II; 8 teeth (0.5%) belonged to demineralization degree III. ③The top three teeth that had the biggest demineralization rates were upper lateral incisors（19.9%）, upper central incisors（14.1%）and the lower lateral incisors （12.2%），while the teeth that had the lowest demineralization rate were the first molars（4.5%）. ④There was no difference between the two groups in dental soft scale degrees before treatment. After treatment, the dental soft scale degrees of the two groups decreased obviously. The group (toothbrushing frequency ≥ 3 times / day ) decreased more obviously (P < 0.05 ). There was no obvious difference between the two groups in demineralization index before treatment, the demineralization index of the two groups rose ovbiously after treatment, and the group (toothbrushing frequency ＜ 3 times / day ) rose more obviously（P＜0.05）.Conclusion The incidence of enamel demineralization in the application of orthodontic fixed appliance is high, especially to the incisors (except the lower central incisors ). Related prevention and timely treatment need to be strengthened.