Abstract: This study explores acute effects of short-term exposure to ambient fine particulate matter (PM_2.5) and ozone (O₃) on hospital visits in the Beijing-Tianjin-Hebei region and surrounding areas and provides epidemiological evidence for the coordinated management of regional air pollution. Daily outpatient visits at 100 hospitals in 14 cities across the Beijing-Tianjin-Hebei region and surrounding areas and daily mean concentrations of PM_2.5 and O₃ as well as meteorological factors for the period from 1 January 2013 to 31 December 2018 are collected. Based on time series studies, a two-stage statistical analysis strategy (generalized additive model combined with meta analysis) is adopted to construct a dual-pollutant model by adjusting confounding factors (such as meteorological factors and time trends) to analyze effects of short-term exposure to ambient PM_2.5 and O₃ on hospital visits. During the study period, the average daily concentrations of ambient PM_2.5 and O₃ are 72.2±56.8 μg/m³ and 58.2±36.9 μg/m³, respectively, and the number of outpatient visits is 62.57 million. The results of the dual-pollutant model show that per 10 μg/m³ increases in 2 d moving average PM_2.5 and O₃ concentrations are associated with excess risks of 0.25% (95%CI: 0.20%—0.29%) and 0.15% (95%CI: 0.07%—0.22%) for daily outpatient visits with 0 to 1 d lag, respectively. Fitting the model of seasonal stratification, the acute effect of PM_2.5 exposure on outpatient visits is strong in cold season, while the O₃-related effect shows a strong effect in warm season. It is found that short-term exposure to ambient PM_2.5 and O₃ in the Beijing-Tianjin-Hebei region and surrounding areas both can increase the risk of outpatient visits. It is recommended to take active measures to coordinately control the combined pollution of PM_2.5 and O₃, and pay attention to different risk characteristics of pollutants between the cold and warm seasons.