Abstract: In order to establish structural damage forecasting method applied to the normalized environmental conditions, the correlation analysis of frequency and seasonal temperature of Runyang Suspension Bridge is performed using health data monitored within 236 days. The analysis results reveal that natural frequencies of higher-order vibration modes remarkably correlate with the seasonal temperature. The daily averaged natural frequencies decrease with the increase of the daily averaged temperature, with an approximate annual variation of about 1.5%―2.0%. The statistically modeling technique using 6-order polynomial is applied to formulate the correlation between the natural frequencies and temperature. The abnormal changes of measured frequencies are detected using the so-called mean-value control chart. The research results show that the proposed method is effective in the elimination of temperature-induced abnormal frequency changes and capable of detecting the damage-induced frequency variations. The proposed method is promising in the identification of structural damage induced modal frequency variations.