This study sought to estimate the association of children's body mass index (BMI) with their social function in Shanghai China. A large population-based cross-sectional study based on a propensity score matching (PSM) analysis was conducted. BMI was compared according to social communication questionnaire (SCQ) classification, and then SCQ score was compared in terms of BMI grouping before and after PSM. A positive SCQ was considered to indicate poor social communication and a negative SCQ was then supposed to be normal. After 1:3 matching, a total of 7563 children aged 3-12 years were included in analysis. There were statistically significant positive correlation of BMI with SCQ scores for obese females of school age (R2 = 0.043, p < 0.001) and negative correlation of these two variables for school-aged females with malnutrition (R2 = 0.047, p = 0.027). In conclusion, BMI may be characterized as one of predictive factor for poor social function of these children.