Abstract: To explore the key factors of overweight based on decision tree model. Methods: 5870 children (3-6 years old) from 23 kindergartens in Nanchang were recruited to measure their height and weight. Then their body mass index (BMI) was calculated, finally their overweight was evaluated according to "The National Physical Fitness Standard Manual (Preschool children part)". Questionnaires were conducted to investigate children's physical activity, children's sedentary behavior, children's birth information, child-rearing methods, parents' body shape and parents' exercise behavior, family situation and other related information, which were divided into 36 variables. The CHAID decision tree model was established by IBM SPSS modeler to screen the key factors affecting overweight of preschool children. Results: The accuracy of CHAID model is 85.23%. The results of CHAID model show that there is a strong correlation between the eight variables with overweight. The most important factor is outdoor physical activity time, father's BMI, mother's BMI, father's income, indoor physical activity time, father's education level, child-rearing methods and TV watching time. Conclusion: Physical activity, especially outdoor physical activity are the most important factors related to preschool children overweight. Parents' obesity and education, child-rearing methods, sedentary behavior are also key factors leading to overweight.

Key words: decision tree, preschool children, overweight