Objective: To analyze the impact of persistent obesity on their lung function, so as to offer insights for implementing intervention measures to increase lung function in obese school age children. Methods: A total of 335 children from the Sheyang Mini Birth Cohort established in 2009 in Yancheng City, Jiangsu Province, who participated in the follow up at the ages of 7 years (2016) and 10 years (2019), were selected as the study participants. Physical measurements including height, weight, and lung function were recorded. According to the World Health Organization standard, that is, gender and age specific to correct the body mass index to calculate the body mass index Z score, was used to evaluate the obesity status of children at the age of 7 and 10. Children were divided into four groups, including sustained non obesity group, restored obesity group, newly classified obesity group, and persistent obesity group. Meanwhile, the lung function prediction equations recommended by the Global Lung Function Initiative were used to standardize the lung function indexes of children. Pulmonary function differences among these groups were examined, and the relationship between childhood obesity and pulmonary function was longitudinally analyzed using generalized estimating equations. Results: The prevalence of obesity were 9.0% and 16.1% at the age of 7 and 10 years, respectively. The proportion of both newly classified and persistent obesity group were 8.1%, respectively. The forced expiratory volume in one second (FEV 1) and forced vital capacity (FVC) were (1 269.90±202.70) and (1 415.70±230.00) mL, respectively, at the age of 7 years. FEV 1 and FVC at the age of 10 years were (1 440.80±403.20) and (1 555.60±517.60) mL, respectively. Cross sectional analysis at age 7 showed that forced expiratory flow at 75% vital capacity (FEF 75 ) ( β=-0.52, 95%CI =-0.96--0.07) and maximal mid expiratary flow (MMEF) ( β=-0.45, 95%CI =-0.89--0.00) were significantly lower in obese children compared to their non obese peers ( P < 0.05). Longitudinal analysis indicated that obese children had lower levels of lung pulmonary function, with a statistically significant difference in FEV 1 ( β=-0.44, 95%CI=-0.85--0.02, P <0.05). There was no significant difference among the various obesity groups ( P >0.05), while gender stratified results revealed significant reductions in FEV 1/FVC in newly classified obese girls at age 10 years ( β=-1.76, 95%CI =-3.13--0.38) and in MMEF in persistently obese girls at age 10 years ( β=-1.44, 95%CI = -2.79- -0.09) ( P <0.05). Conclusion Obesity may contribute to reduced lung function levels in school aged children, with newly classified and persistent obesity having more pronounced effects on lung function in girls.