Objective To study the correlation between overweight and obesity and lung function in children with asthma. Methods A total of 368 children with asthma attending the respiratory outpatient clinic from July 2022 to September 2022 were selected and categorized into 235 cases (63.8%) in the non-overweight and obese group, 57 cases (15.5%) in the overweight group, and 76 cases (20.7%) in the obese group according to the body mass index (BMI), and the indexes of lung function were tested in the three groups of children. These included forced vital capacity (FVC), forced expiratory volume at the end of the first second (FEV₁), one-second rate (FEV₁/FVC), forced expiratory flow rate (FEF) accounted for 25%, 50%, 75% of forced vital capacity (FEF₂₅, FEF₅₀, FEF₇₅), forced expiratory flow rate in the middle period (FEF_25-75), peak expiratory flow (PEF). Results Among overweight and obese children, the proportion of poorly controlled asthma was higher, and the difference was statistically significant when compared with the non-overweight and obese group (P<0.05). Among 368 children with asthma, BMI values were negatively correlated with FEV₁/FVC (r=-0.22, P<0.05) and positively correlated with each of the FVC, FEV₁, FEF₂₅, FEF₅₀, FEF₇₅, and FEF_25-75 (P<0.05). In children with acute exacerbation and remission, the results of correlation between BMI values and lung function indicators were the same as before. Conclusions The proportion of poorly controlled asthma was higher in overweight and obese children. With the increase of BMI, the FEV₁/FVC of children with asthma showed a decreasing trend. Therefore, the negative effects of overweight and obesity on children with asthma were mainly manifested in the central airway.