〔Abstract〕 Objective To explore the effects of pre-pregnancy BMI and gestational weight gain on the measure-ment indexes of obesity in preschool children, and provide evidence for weight management of pregnant women. Methods 1 769 pregnant women who underwent prenatal examination in maternal and child health institutions were selected as the study subjects. “Maternal and Child Health record form during pregnancy and delivery period” and the hospital electronic medical system were used to collect information such as pre-pregnancy body mass index(BMI) and gestational weight gain(GWG). The “Health and behavior record of Preschool Children” was used for childhood follow-up to collect information such as physical activity of feeding patterns of preschool children. Physical examination on collected physical measurement data such as upper arm circumference, upper arm skinfold thickness, abdominal wall skinfold thickness, height and weight, and described the distribution of related characteristics and the effects of pre-pregnancy BMI and weight gain during pregnancy on the measurement index of obesity in preschool children. Results The number of pregnant women with excessive GWG are 770, accounting for 50.7%. There were statistically significant differences in Pre-pregnancy BMI(χ2=46.08,P<0.01), annual family income(χ2=15.07), number of pregnancies(χ2=12.22) and different pregnancy attitudes(χ2=19.05) among different GWG groups. After adjusted confounding factors such as education and education, pregnant women with excessive GWG was positively correlated with upper arm circumference of preschool children(β=0.091, 95%CI: 0.118 to 0.505), upper arm skin fold thickness(β=0.086, 95%CI: 0.217 to 1.067), abdominal wall skinfold thickness(β=0.059, 95%CI: 0.014 to 0.938) and age-specific BMI(β=0.150, 95%CI: 0.205 to 0.456). The pre-pregnancy low BMI group and upper arm circumference of preschool children(β=-0.182, 95%CI:-0.896 to-0.522), upper arm skinfold thickness(β=-0.138, 95%CI:-1.586 to-0.758), abdominal wall skinfold thickness(β=-0.118, 95%CI:-1.563 to-0.638), age-specific BMIZ score(β=-0.182, 95%CI:-0.588 to-0.342) were negatively correlated. Conclusion Excessive GWG is a risk factor for obesity in preschool children, and lower pre-pregnancy BMI is a protective factor for obesity in preschool children.