The voltage generator equipment is not conductive to resist horizontal seismic actions and strong wind actions for its large slenderness ratio, high center of gravity and low damping ratio. To study the damping matrix models in seismic response analysis of the generator, the dynamic characteristics of a twin-tower voltage generator were analyzed under the excitations of three waves (Taft wave, El-Centro wave and Ninghe wave) with six different Rayleigh damping modes. The results show that the selection of damping coefficients has great influences on the calculation accuracy of structural dynamic responses. As the damping coefficients are determined by the two natural frequencies of vibration, it is wiser to take both characteristics of seismic spectra and structural natural vibration properties into account when choosing the damping coefficients, so that the calculation results will be more accurate.