Abstract: By using the near-ground ozone concentrations and simultaneous meteorological data in Tianjin from 2017 to 2021, a localized ozone meteorological composite index was constructed based on statistical methods, and the contributions of meteorological and anthropogenic factors to changes in ozone concentration and exceedance days were assessed. The results showed that the ozone meteorological composite index could be well established based on the daily maximum temperature, sea level pressure, average wind speed, relative humidity, boundary layer thickness and short-wave radiation flux, and the correlation coefficient with the actual ozone concentration could reach 0.86 (P<0.01), which was higher than any single meteorological factor. Based on the evaluation of this index, the ozone concentration in Tianjin showed an increasing trend at first and then a decreasing trend from 2017 to 2021, with a decrease of 15.9% in 2021 compared to 2017. Anthropogenic factors played a dominant role in the concentration change, contributing 10.0%, while meteorological factors contributed 5.9%. The change in the number of exceedance days in the five years was consistent with the trend of concentration change, and mild pollution was the main type of exceedance days. The high proportion of mild pollution in 2018 was the main reason for the highest number of ozone exceedance days in that year. The number of ozone exceedance days in Tianjin decreased by 36 days from 2017 to 2021, with meteorological conditions contributing to a decrease of 20 days and anthropogenic factors contributing to a decrease of 16 days. The analysis of the factors affecting changes in the number of exceedance days at different pollution levels showed that meteorological conditions were the main factor leading to a decrease in mild pollution days, while the contribution of anthropogenic control measures was mainly reflected in the reduction of moderate pollution weather.