Objective　To investigate the effect of body weight on pulmonary function in children. Method　According to the World Health Organization's overweight and obesity standard for children, the obese, overweight and normal weight children were selected and grouped from children with neither respiratory disease nor other diseases affecting pulmonary function. Their pulmonary ventilation function were measured and compared. Results　A total of 1233 children were included, including 285 obese children, 155 overweight children and 793 normal weight children. There were significant differences in VCMAX and FVC among the three groups (P<0.01), and they were the highest in the overweight group. The differences of FEV1/VCMAX, FEV1/FVC, FEF75 and MMEF25-75 among the three groups were statistically significant (P<0.01) and they were the highest in the control group. There was no significant difference among the three groups in lung ventilation indexes of FEV1, PEF, FEF25 and FEF50 (P>0.05). The actual values of lung function were similar to the ones above among the three groups but the degree of changes were smaller to some extent. Conclusions　Overweight and obese children have increased lung capacity compared to the children with normal weight, and they may also have obstructive disease and small airway dysfunction.