Dental caries in preschool children is prevalent worldwide, but data regarding its magnitude and associated factors were not available for preschool children in Zhejiang Province, China. This study examines the dental caries situation and its associated factors in Zhejiang Province. A total of 1591 children aged 3–5 years and their parents or caregivers were enrolled in this study. The condition of their teeth was assessed by three dental technicians qualified to WHO 2013 criteria. A structured questionnaire was completed by the children’s parents or caregivers. A logistic regression analysis was used to analyze the risk factors that may be associated with dental caries occurring among preschool children. Caries prevalence (dmft> 0) of 3–5 year old children in Zhejiang Province was 70.4%. The mean decayed, missing and filled teeth (dmft) scores of the 3, 4 or 5 year old children surveyed were 2.96 ± 4.07, 4.42 ± 4.66, and 5.75 ± 5.19 respectively. The negative binomial regression model found that higher dental caries prevalence was found in children as age increased, with lower body mass index (BMI), with longer breastfeeding duration and with fewer hours of sleep. The dental caries prevalence and dmft score of 3–5-year-old children in Zhejiang Province was high, and it was associated with age, BMI, breastfeeding duration and hours slept.