A quasi-zero stiffness (QZS) torsional vibration damper is proposed for heavy-duty vehicles to provide a solution to the contradiction between the high static stiffness required for system load bearing and the low dynamic stiffness needed for vibration isolation. The pre-compressed connecting rod-disk spring is designed as a negative stiffness mechanism to provide torsional negative stiffness in order to offset the positive stiffness generated by the cylindrical spring. A nonlinear mathematical model of the quasi-zero stiffness torsional isolator is established, and its dynamic characteristics are analyzed using the Harmonic Balance Method. Folded frequency-amplitude curves and vibration transmissibility of the system at different frequencies are obtained. Meanwhile, the vibration effectiveness of the QZS torsional isolator is evaluated under the designed torque. The results show that the isolation effect of the QZS isolator is significantly superior to that of linear isolators within the low-frequency range.