Aero-dynamic damping ratios are significant parameters with which to accurately evaluate the wind dynamic responses of a transmission tower with and without lines. Based on the displacement and acceleration time series obtained by the full aero-elastic model wind tunnel, the first and second mode shape structural and aero-dynamic damping ratios of the electrical transmission tower with and without lines are evaluated respectively, by combining the empirical mode decomposition (EMD) method, wavelet analysis, random decrement technology (RDT) and Hilbert transform. In the meantime, the change rules of the structural and aero-dynamic damping ratios are analyzed. The results show that the structural damping ratios of the transmission tower with lines are larger than those without lines, and the aerodynamic damping ratios of the tower decrease with frequency while increasing with wind speeds. Furthermore, the empirical formulae to evaluate the aero-dynamic damping ratios of towers under the test wind speed are proposed based on the least mean square method.