In this paper, the flexibility method of damage identification for transmission tower based on Wigner-Ville Distribution (WVD) signal amplitude vector is forwarded. The damage coefficient equation involving modal parameters and damage parameters is firstly established, on the basis of the linear relation of flexibility matrix and structure parameters. Then, the mathematical deduction of WVD signal term reveals the function relation between WVD signal terms and modal parameters. Lastly, the damage coefficient equation is solved by substituting mode shape vector with the signal amplitude vector of response under suddenly unloading to identified the position and extent of structural damage. A numerical example demonstrates its accuracy for damage identification and excellent noisy immunity.