Based on prototype tests of flexible flanges for long-span electric transmission tower in Wusongkou, the forced process, failure pattern, load bearing-capacity and deformation etc of flexible flanges are systematically studied, and the influence of thickness of flanges, distance between bolts and edge of flanges, and diameter of bolts on behaviors of flanges and welding seams are also investigated. The studies show that the flexible flanges have good behaviors and their use in Wusongkou tower (500kV) is validated.