Obesity has become a major disease that affects children. The incidence of obesity has been increasing year by year. Although a lot of studies have been done in many countries and regions on the current situation and epidemiological trends of childhood obesity, there is a lack of uniform diagnostic criteria. Due to the different indexes and methods chosen, the evaluation of the incidence of obesity in the same population will come to different conclusions. This paper introduces several diagnostic indicators commonly used at home and abroad. 1, height standard weight method for the WHO recommended one of the methods. (also known as height and weight) is the best indicator to evaluate the obesity of children before puberty (under 10 years old), so in 1978 to the world recommended the use. This method is based on height. The 80th percentile of the same height population is used as the standard weight of the height population. More than the standard weight of 20% to 29% for mild obesity, 30% to 49% for moderate obesity, more than 50% for severe obesity. This method is widely used in China. Other Asian countries except Japan also generally use this method to determine the obesity of children. The advantage of this method is simple, easy to grasp, intuitive, easy to use. It also eliminates the influence of race, genetic and regional differences and developmental level. In children under 10 years of age this index can basically represent the body fat content, that is, when the height standard weight exceeds 20% corresponds to the amount of body fat more than 15% of the normal fat content [1]. In China, the reference standards currently in use are the standard weight for height recommended by WHO in 1985 and the standard weight for height of children in nine urban areas in China in 1995. However, the relationship between height and weight fluctuates greatly in children and adolescents above the age of 10 years, as the body morphological indicators and body composition change significantly. For a certain determined height value, the weight value of different age groups is very different. Therefore, for children and adolescents above 10 years old, the method cannot be used to evaluate obesity or not. 2, body mass index method (BMI) that weight (kg) divided by the height of the square (m2), and pediatrics commonly used Kaup index (g/cm2) for the same meaning. This index is a simple, easy and commonly used index to evaluate obesity and wasting in adults, and is widely used internationally. Some studies have shown that population BMI can predict the risk of disease and death. In adults, BMI has an asymmetric U-shaped relationship with the risk of disease and death. For example, BMI below 185 is negatively correlated with the risk of disease and death in Western Caucasian populations, the risk of disease and death begins to rise above BMI 25, and the risk of disease and death increases steeply above BMI 30, while BMI values between 185 and 249 are in the appropriate range. Therefore, WHO recommends that BMI&ge 25 be defined as overweight for adults and BMI&ge 30 as obese for adults. Due to racial differences, the appropriate range of BMI values for Asian populations is shifted to the left compared to Westerners. It is suggested that a BMI of 17 to 23 is the appropriate range for Asian adults. Generally, BMI&ge 23 is considered to be overweight and BMI&ge 25 is obese for adults. 2003 ILSI China Office/China Obesity Working Group proposed BMI&ge 24 and BMI&ge 28 as the diagnostic criteria for overweight and obesity for Chinese adults, respectively. The adult BMI standard is also not suitable for children and adolescents aged 10 to 18, because the relationship between BMI and body fat percentage depends on the maturity level, and the growth spurt and sexual development level of adolescents are signs of maturity level, and there are obvious age-sex differences. Therefore, WHO recommends the use of age-sex BMI to evaluate overweight and obesity in adolescents aged 10 to 24 years. According to the age-sex BMI percentile curve and age skinfold thickness percentile curve established by Must et al, the 85th percentile of BMI&ge was defined as the risk of overweight, and obesity was defined if the 85th percentile of BMI&ge was accompanied by the 90th percentile of triceps skinfold thickness and subscapular skinfold thickness&ge. It can be seen that the use of BMI to determine obesity in children and adolescents is best evaluated in conjunction with other indicators. The International Obesity Task Force (IOTF) actively advocates the development of international unified BMI diagnostic criteria for overweight and obesity in children. 2000 IOTF used the cross-sectional survey data of children aged 0 to 18 years in six countries and regions, including Brazil, Britain, Singapore, the United States, the Netherlands and Hong Kong, as the reference population for establishing international BMI cut-off points for children. The international diagnostic criteria of age-sex BMI for overweight and obesity in children aged 2 to 18 years were proposed. The possible problems of this standard are also pointed out. Firstly, the criteria were established based on BMI&ge 25 for overweight and BMI&ge 30 for obesity in adults, and the BMI curves for children aged 2 to 18 years were drawn based on the results of six groups of surveys, summed and averaged to determine the BMI cut-off points for overweight and obesity in children of specific age-sex groups. Due to the lack of information on the relationship between adolescent obesity and future diseases, the index can only provide statistical data and has some limitations in practical application. The second issue is the representativeness of the selected sample. The majority of this reference population is from the West, while the samples from Asia and Africa are relatively small. Ethnic differences, developmental patterns, and living standards all have an impact on BMI values. For example, children in China and India are relatively short in stature, and children in mainland China have delayed pubertal development compared to children in Hong Kong, which may result in misclassification when applying this diagnostic criterion. It is the consensus of most scholars that different populations should use reference values appropriate for their own populations. For this reason, many scholars in China have done a lot of work to establish the BMI standard for obesity in Chinese children. Based on the data of 4574 children in Shenzhen, the standard reference value of obesity for children aged 7-12 years in Shenzhen was established. It is considered that the BMI cut-off point of obesity for male and female children in the region is the 85th percentile and 90th percentile respectively, and the BMI value of school-age children increases with age. Based on the 1995 survey data in Shaanxi Province, the LMS method was used to fit the percentile curves to obtain the 952nd and 945th percentile BMIs for overweight and 995th and 998th percentile BMIs for obese children aged 0-18 years in Shaanxi Province, respectively, suggesting that children in Shaanxi Province have a thin physique. Ji Chengye et al. suggested the 85th and 95th percentiles as the diagnostic cut-off points for overweight and obesity in children and adolescents aged 7 to 18 years based on the 2000 national health and fitness study of adolescents aged 6 to 18 years. BMI is a good indicator for screening obesity in children over 10 years of age based on many studies. The relationship between BMI and body fat has a direct impact on the accuracy of screening obesity in children, and the increase of body fat is the direct evidence of obesity. The relationship between BMI and body fat has a direct impact on the accuracy of screening for obesity in children.