Nonlinear finite element model of a transmission tower-line system is set up and galloping of the iced quad bundle conductors in the system is numerically simulated by means of ABAQUS software. Based on the galloping orbits, vibration amplitudes and response frequency characteristics of the conductors, it is found that the deformation of the towers in the system greatly changes the orbits and vibration amplitudes of the conductors, but has a little effect on the frequency characteristics of the galloping responses. The maximum stresses of the conductors and towers during galloping are smaller than the material strength, which means that the failure of the conductors and towers induced by galloping is usually fatigue failure.