Objective To explore the effect of fine particulate matter (PM_2.5) in Taiyuan City on short-term pulmonary function in elderly patients with chronic obstructive pulmonary disease (COPD). Methods Among the 1 015 elderly COPD patients admitted to the respiratory departments of five general hospitals in Taiyuan City from December 2021 to December 2023 were retrospectively selected for research; medical records, air pollutant data and meteorological data were analyzed; the relationship between PM_2.5 and lung function indicators and air pollutants was analyzed; the impact of PM_2.5 on lung function and its lag effect were analyzed; the cumulative effect of PM_2.5 concentration on the risk of pulmonary ventilation dysfunction was analyzed; The influence of gender and age on the relationship between PM_2.5 and patients ' short-term pulmonary function was analyzed. Results PM_2.5, respirable particulate matter (PM₁₀), sulfur dioxide (SO₂), carbon monoxide (CO) were negatively correlated with average temperature and average humidity (P<0.05) ; Nitrogen dioxide (NO₂), ozone (O₃) were negatively correlated with average temperature (P<0.05) ; There was a positive correlation among PM_2.5, PM₁₀, SO₂, CO, NO₂, and O₃ (P<0.05) ; Elevated PM_2.5 is an independent risk factor for decreased lung function and increased air pollutants (P<0.05) ; At lag0 and lag1, PM_2.5 concentration was negatively correlated with lung function in a dose-response manner (P<0.05); daily average PM_2.5 concentration at lag0 was a dangerous effect (P<0.05). Conclusion The impact of PM_2.5 concentration on lung function has a certain time lag. An increase in PM_2.5 concentrations can lead to a decline in lung function.