【Objective】 To investigate the status of early childhood caries and caries-related factors for 3 years old children in the Haidian District of Beijing. 【Methods】 The investigation was involved in 588 children of 3 years old form 12 preschool in the Haidian District in Beijing. Their caries were examined and questionaire was provided by their parents. 【Results】 The prevalence of early childhood caries was 47.6%.The mean dft score was 2.20. The children with dft value greater than 3 occupy 26% of the entire examples whereas the number of their dft was 76% of the total caries. Logistic regression analysis showed that the feeding habits, the level of saliva mutans streptococci and the duration of feeding were significant. 【Conclusions】 3 years old children who have just entered kindergarten have a high rate of early childhood caries and low rate of treatment. A few children have a higher risk of early childhood caries and more attention should be need to them, check for them as soon as possible, meanwhile do a better job in prevention.