Abstract: The modal frequency is a commonly used index to reflect the global condition of a bridge. However, the field measurements have shown that the modal frequency would vary significantly with the operational and environmental actions, even if the bridge is in a good condition. Hence, it is necessary to investigate the action-frequency correlation of bridges in order to eliminate the normal frequency variation and then highlight the anomaly-induced frequency changes. Based on long-term monitoring data, this study simultaneously examined the periodic variability of the high- and low-order frequencies of Donghai Bridge. The periodic characteristics exist in the variation of both the high- and low-order frequencies, and the dominant cycles of modal frequencies coincide with those of the operational and environmental actions. The structural temperature and traffic loading exert a larger influence on frequency changes than the other actions. All the modal frequencies of Donghai Bridge have a negative correlation with the temperature change, while the correlation between frequencies and traffic loading seems to depend on the order of each mode.