Obesity has an increasing trend worldwide. Body mass index (BMI) is a common method of judging obesity, but the research of judging the appropriate bodyweight of Chinese children aged 3 to 6 years is still lacking. Bioelectrical impedance analysis (BIA) is a safe, accurate, reliable and inexpensive method for screening the overweight and obesity. In this study, preschool boys( n= 392)and girls(n= 309) aged 3 to 6 years, recruited from kindergartens in Zhejiang province of China, completed a survey of BMI and BIA measured by InBodyJ20. Pearson correlation analysis of the correlation between BMI and BIA, and linear regression method analysis of BMI and BIA. The linear relationship between rates and construct a regression equation, using the Kappa coefficient to test the consistency of BMI and body fat rate. The BMI of boys and girls decreased from 19.2±4.9 and 18.1±2.4 at the age of 3 to 14.1±3.3 and 15.1±3.3 at the age of 6，and showed a downward trend as the age increased. Analyzing the correlation between BMI and body fat percentage, it is 0.533 for boys and 0.539 for girls. The Kappa coefficient test results of BMI and body fat percentage showed that Kappa value=0.339(P<0.05), indicating that the diagnostic results of BMI and body fat percentage were consistent, but the consistency was general.