Abstract: Objective To analyze the effect of gestational weight gain on macrosomia, and provide evidence for the reasonable management of pregnancy weight. Methods A case-control study was set up based on the “ Mother and Child Health Monitoring”project. The follow-updata during late pregnancy andtheir one-month children was obtained from monitoring points in five provinces and counties in China. Women in the third of pregnancy were recruited to fill out the questionnaire. Then, they received a prospective observation, which started from trimester and ended at one month after giving birth. They were required to fill the questionnaire of the newborn. The variables of delivery gestational week, birth weight and gender information in the one newborn questionnaire were obtained from the medical records. According to the pregnancy outcome, 2 597 pregnant women were divided into macrosomia group(192) and control group(2 405). Finally, a design of case-control study was used for analysis. Chi-square test or Fisher exact probability method was adopted to compare the differences between groups. Multivariable logistic regression was applied to analyze the relationship between gestational weight gain and macrosomia. Taking pre-pregnancy body mass index as a layered factor, multivariable logistic regression was applied to determine the association of gestational weight gain with macrosomia. Results A total of 2 731 pregnant women were followed up in this study with a follow-up rate of 100%. After data cleaning, 2 597 were included in the analysis. After adjusting for maternal age, maternal education, annual family income, gestational diabetes, gestational age, and neonatal sex,overweight or obesity before pregnancy(OR= 2. 43, 95% CI: 1. 65-3. 56) and excessive gestational weight gain(OR=2. 18, 95% CI: 1. 46-3. 27) were independent risk factors for macrosomia. Stratified analysis showed that the pregnant women with normal body mass index(18. 5 kg/m²≤BMI < 24. 9 kg/m²) before pregnancy had a higher risk of macrosomia if they gain excessive weight during pregnancy(OR= 2. 07, 95% CI: 1. 27-3. 37). For pregnant women with overweight or obesity(BMI≥25. 0 kg/m²) before pregnancy,gaining excessive weight during pregnancy(OR= 2. 63, 95% CI: 1. 07-6. 47)also increased the risk of macrosomia. Conclusion Excessive gestational weight gain is an independent risk factor for macrosomia. Excessive weight gain during pregnancy will increase the risk of macrosomia among those with normal weight, overweight or obesity before pregnancy.