Objective: Comparing the body composition status of pregnant women to look for a reliable detection indicator of obesity during pregnancy, accurate assessment of the nutritional status of pregnant women and a reasonable medical nutrition intervention to improve pregnancy outcomes.Methods: we use body composition analyzer to measure proteins, salts, overall water, muscle mass, skeletal muscle, body fat, body fat percentage, waist-hip ratio of fat, bone mineral content ,Visceral fat area and Basal metabolism of pregnant women Aged 26 to 30 years old which have the maternity medical examination in our hospital from June to August in 2012. Divide them into two groups: 251 cases of 20-24 pregnant weeks and 132 cases of pregnant 28-32 pregnant weeks. Compare the differences of maternal body composition between these two groups.Outcomes: Proteins, salts, overall water, muscle mass, body fat, bone mineral content, visceral fat area and basal metabolism significantly increased within the increased pregnant weeks, There are statistically significant differences between the two groups. There is no significant difference between the two groups of pregnant women in skeletal muscle, body fat percentage andwaist-hip ratio.Conclusions: Body fat percentage, waist-hip ratio of pregnant women does not change within increasing gestational age. They are reliable indicators of evaluating whether pregnant women are obesity or not. We can use these to assess the nutritional status of pregnant women, give reasonable medical nutrition interventions, scientific regulation of fetal birth weight to improve pregnancy outcomes.