The purpose of the 3rd national survey on childhood obesity was conducted not only to understand the present status and trends of childhood obesity in China since the last survey conducted 10 years ago, but also to reveal the health status of preschool children at nutrition transit period and to evaluate the efficacy and sensitivity of cited reference population, criteria and cut-off point of body mass index (BMI), adiposity rebound age, waist/hip ratio and other parameters relevant to the diagnosis of obesity made by the national task force on childhood obesity of China (NTFCOC). A total of 84,766 children aged 0 - 7 years were recruited in the survey by the random cluster sampling which represented a 1, 414, 220 children's population from 11 cities covered north, central, south and west regions of China. The criteria of screening overweight/obesity was more than 1 Z-score/2 Z-score of the medium of reference value of weight for height made by WHO. Length-height/weight for all subjects and waist/hip/thigh circumference and blood pressure data for children 3 - 6 years of age were measured. The prevalence of overweight and obesity, overweight-obesity ratio, adiposity rebound age and BMI were calculated. The enumeration and measurement data were statistically managed by chi-square test and T-test, respectively using SPSS version 12.0 and the significance level was 0.05. (1) The prevalence of obesity and overweight was 7.2% and 19.8% for all; 8.9% and 22.2% for boys, and 5.3% and 17.0% for girls, respectively, which is 3.6/4.7 times higher than that of 1996 respectively, the annual increase rate of obesity and overweight was in average 156% and 52%, respectively. The distribution pattern of prevalence of overweight and obesity in geographic areas and gender was that the northern regions had higher prevalence than the west and the central regions and the prevalence in boys was higher than in girls. The obesity/overweight ratio (OOR) was still at a high risk level. (2) BMI at 1 month after birth was higher than 16.5, then increased to the top of 17.8 at 1 year of age and decreased to the bottom of 15.7 at 5.5 years of age and increased a little since then. It was never higher than 18 of diagnosis point of obesity during the preschool age period. (3) The adiposity rebound age was 5.5 years of age in this study and delayed half a year as compared with that seen in 1999. The adiposity rebound ratio at first half year after birth (ARR1) was 0.56 and 0.97 at second half year after birth (ARR2) which is an acceptable level according to the cut-off point made by NTFCOC and lower than the level obtained 10 years ago. (4) The pseudo-overweight phenomenon can be seen in the western regions which was derived from linear growth retardation and showed that both the malnutrition and obesity are a health problem in the poverty and maintain area of the western regions.(5) The 12.9% of obese children who's blood pressure was higher than 95th percentile of reference value and 17.2% of them had a waist/hip ratio higher than 1.0 which is a warning point for the risk factor of CHD made by the NTFCOC. (6) The data showed that all the reference population and it's cut-off point for BMI, adiposity rebound age/ratio, waist/hip ratio etc. made by NTFCOC is valuable, reliable and practicable. The prevalence of childhood obesity and high blood pressure in obese children has been increased sharply during the recent 10 years, which is a out of control and a severe hazard to obese children. The early prevention and management of childhood obesity is urgently needed.