Objective: To analyze the trend of percentile changes in body composition among children and adolescents aged 7 to 18 by gender and age, and to provide a scientific basis for reference value. Methods: A stratified cluster random sampling method was used to select 1 585 children and adolescents from September to December 2020. Use the GAMLSS to estimate the P 25 , P 50 and P 75 percentile value of gender, age specific body fat percentage (BF%), fat mass index (FMI) and fat free mass (FFM). Results: In different age groups, body fat percentage of boys with normal nutritional status peaked at around 10-year old, among them, body fat percentage of 10-year old P 25 , P 50 and P 75 were 22.2%, 26.1% and 30.1%, respectively. Body fat percentage of obese boys was at a high level. Among girls, body fat percentage under different nutritional status did not change. With the increase of age, fat mass index plateaued slightly in normal and overweight boys. However, in obese boys, with the increase of age, FMI gradually increased with the increase of percentile, while the value of FMI gradually decreased in girls. Whether in boys or girls, with the increase of age, fat free mass index shows an increasing trend, and boys increase faster. Conclusion Under different nutritional status, there are differences in the percentile value of body fat percentage, fat mass index and fat free mass by gender and age, which can provide a scientific basis for reference value of body composition in children and adolescents.