Abstract: Objective To observe the effect of fluoride foam on dental caries increment in primary teeth, and provide the basis for prevention and control of children's dental caries. Methods Three hundred and thirty-five children were included randomly from junior classes of 4 kindergartens as experimental group, and another 268 children from junior classes of another 4 kindergartens as control group. The experimental group used 1.23% fluoride foam twice a year, and the control group did not have any interventions. The two groups of children were followed up for 3 years, and examined for the situation of their caries detection rate and average risk of caries, and for evaluation of the effect of fluoride foam in prevention of children's dental caries. Results Caries detection rate in the two groups increased with age. After 3 years, caries detection rate in control group increased by 34.05% and in experimental group increased by 22.19%. The use of fluoride foam reduced 10.89% caries disease for experimental group. Caries detection rates were 55.62% in experimental group and 66.51% in control group. The difference in detection rate was significant between experimental group and control group (P<0.05). Average caries in experimental group was 3.4±4.38 after 3 years, and 4.7±4.80 in control group. There was a significant difference in average caries between the two groups (P<0.05). Conclusion Application of 1.23% fluoride foam was effective in reducing the increment of dental caries in primary teeth, and it is worth promoting in the kindergartens.