Abstract: The external low-velocity impact identification problem was investigated on a cylindrical stiffened composite structure. The piezoelectric sensors were used to obtain the stress wave signals when the structure was impacted by a foreign object with low-velocity. Aiming at the problem that the impact location identification of a stiffened composite structure and especially the location identification when the impact occurring near edges of the monitoring region, a two-step positioning method based on the power of sensor signals was proposed to estimate the impact location. The impact force was reconstructed by the system-identification method, furthermore, the relationship between the model order of the transfer function and the correlation coefficients was analyzed and the principle of the model order selection was suggested to supplement this method. The results indicate that the proposed positioning method can estimate impact locations with high precision regardless the impact occurring region, and the improved system-identification method can identify the location and force time history effectively when an impact event doesn’t occur in the region with stiffener; however, when an impact occurring on the region with stiffener, the impact can not be well identified due to the complex influence of stiffeners on stress wave propagation.