This study mainly makes test and analysis through the experimental test method for one two three grade 126 students body fat status. The main conclusions are different ages primary abdominal obesity, body mass index does not increase with age and growth, increasing of body weight is mainly to the amount of muscle growth; height, muscle mass, standard body weight, age, body mass index exist difference in each age group; body fat mass, body fat rate index of girls are higher than boys, and other indexes of boys were higher than the girls; elementary school students of different sex ratio in muscle mass, body fat, body mass index exist very significant difference.