Previous studies have found that fine particulate matter (PM2.5) air pollution is associated with decreased lung function. However, most current research focuses on children with asthma, leading to small sample sizes and limited generalization of results. The current study aimed to measure the short-term and lag effects of PM2.5 among school-aged children using repeated measurements of lung function.This prospective panel study included 848 schoolchildren in Zhejiang Province, China. Each year from 2014-2017, two lung function tests were conducted from November 15th to December 31st. Daily air pollution data were derived from the monitoring stations nearest to the schools. A mixed-effects regression model was used to investigate the relationship between PM2.5 and lung function. The effect of PM2.5 on lung function reached its greatest at 1-day moving average PM2.5 exposure. For every 10 μg/m3 increase in the 1-day moving average PM2.5 concentration, Forced Vital Capacity (FVC) of children decreased by 33.74 mL (95% CI: 22.52, 44.96), 1-s Forced Expiratory Volume (FEV1) decreased by 32.56 mL (95% CI: 21.41, 43.70), and Peak Expiratory Flow (PEF) decreased by 67.45 mL/s (95% CI: 45.64, 89.25). Stronger associations were found in children living in homes with smokers. Short-term exposure to PM2.5 was associated with reductions in schoolchildren's lung function. This finding indicates that short-term exposure to PM2.5 is harmful to children's respiratory health, and appropriate protective measures should be taken to reduce the adverse effects of air pollution on children's health.