Objective: To investigate the prevalence of dental caries of 4-year-old children in Miyun District of Beijing by international caries detection and assessment system (ICDAS), to detect the caries activity Cariostat value and to analyze the correlation between the Cariostat value and dental caries. Methods: Totally 815 children aged 4 years in 7 kindergartens in Miyun District of Beijing were recruited. The clinical examination of all children was conducted by one examiner using ICDAS. The oral de-birs and plaques were collected by one doctor who recorded the Cariostat scores. The results of clinical examination were compared between genders. At the same time, the prevalence of dental caries, the mean d_3-6ft/d_3-6fs and d_1-6ft/d_1-6fs among high Cariostat scores group (2.0-3.0), medium Cariostat scores group (1.5) and low Cariostat scores group (0-1.0) were compared. The distributions of incipient caries in different Cariostat scores groups were compared among children with incipient caries only. Results: All the children had incipient caries, and 78.3% of the children had cavitated caries with ICDAS score of 3 or above. The mean d_1-2t scores were 9.76±3.65, the mean d_3-6ft scores was 4.64±4.43 and the mean d_1-6ft scores were 14.41±3.42. The incipient caries with ICDAS score of 1-2 were widely distributed, accounting for 67.7% of the total numbers of caries. There was no significant diffe-rence in caries prevalence and caries experience between genders (P>0.05). The proportion of children with high Cariostat scores in boys (43.6%) was higher than that in girls (33%) and the difference was statistically significant (P<0.05). With the increase of Cariostat scores, the prevalence of cavitated caries, the mean d_3-6ft/d_3-6fs and d_1-6ft/d_1-6fs scores in children was on the increase and the difference among the three groups was statistically significant (P<0.05). For children with incipient caries only, the distribution of incipient caries in different Cariostat scores groups was no significant difference (P>0.05). Conclusion: ICDAS can detect early enamel demineralization of deciduous teeth in children. The prevalence of dental caries among 815 4-year-old children in Miyun District of Beijing is more serious, and incipient caries is widely distributed in children. Cariostat value reflects the status of cavi-tated caries and has no correlation with the distribution of incipient caries. Therefore, the combined application of ICDAS and Cariostat caries activity detection method is helpful for the detection of incipient caries and screening of caries high-risk children, which has great significance for the comprehensive ma-nagement of caries in children and the formulation of early preventive measures.