The objective of the paper is to present a method for structural damage presence detection from the time-varying modal parameters identified from the seismic response records in great earthquake. The time-domain system identification method RARX (Recursive Auto-Regression with exogenous variables) model is adopted to identify the time-varying parameters including modal frequencies and damping ratios from the seismic response data. Then the damage presence is detected from the change of parameters during earthquake. A 7-story reinforced concrete building, which had suffered moderate damage and recorded seismic response in Chi-Chi Earthquake, is used for the analysis. It is found that the damage presence can be determined from the decrease of the modal frequencies or the increase of damping ratios, and the time at which the building is damaged can also be detected from the time-varying modal frequencies. The results can be considered as the supplement materials for structural safety evaluation, structural damage investigation and related works.