Abstract: The statistic method for system identification in civil engineering is defined, and different identifications are performed based on different dynamic responses. The experimental and numerical data of a frame structure were investigated. The statistical features of the acceleration were inspected on the probability density; the modal shapes were also inspected on the standard deviation. It is concluded that characteristic features are not sufficient for the identification. The damage conditions were identified by the Statistical Process Control theory with a confidence level. Furthermore, the conditions were identified using the Principle Component Analysis method based on the acceleration and the modal data respectively.