The excitation device is the core device of the trapezoidal thread vibration-assisted cold extrusion machine, which is a new type of mechanical torsional vibration device based on the torque balance state. On the basis of introducing its structural principle, the dual effect of auxiliary vibration on the trapezoidal thread cold extrusion process is analyzed. On the one hand, the change of the taper angle amplitude in the whole process is explored, as well as the influence of the spindle speed and the excitation frequency on the tap angle. It is concluded that the vibration of the excitation device is effectively transmitted to the working part of the tap. On the other hand, through the frequency domain analysis of machine signals under different operating conditions, the excitation device does cause the forced vibration of machine parts. Finally, by comparing the processing quality and the processing surface quality of the trapezoidal thread obtained by the traditional cold extrusion method and the vibration-assisted cold extrusion method, it is concluded that the auxiliary vibration of the exciting device is dominated by the beneficial effect.