In this paper, the initial disc thickness variation (DTV) of a ventilated disc in automotive brake system is modeled as sinusoidal function of the second order. The transient thermomechanical coupling properties of the brake system is simulated using finite element (FE) modeling. The system models and results were verified by a thermomechanical coupling test of a disc brake conducted on a brake dynamometer. By using varied evaluation indexes such as the temperature distribution, the normal stress and the elastic deformation of disc surfaces, the influences of the initial DTV and its direction as well as its amplitude on the thermomechanical coupling characteristics were analyzed. The simulation results show that the distribution of temperature and the normal stress in circumferential direction exhibit the same sinusoidal function of the second order as the modeled initial DTV property, which is different from the thermomechanical coupling characteristics caused by disc surface initial run-out (LRO). Whereas the thermomechnical coupling property of the disc in circumferential direction exhibit the same sinusoidal function of the second order as that of the initial DTV, the distribution of the temperature, the normal stress and the elastic deformation in radial direction are found to be uniform. The changes in the magnitude of initial DTV are found to have insignificant effects on the changes in the overall thermomechnical coupling property. However, the circumferential gradients of the temperature, the normal stress, and the maximum disc distortion increase linearly with the increase of the magnitude of the initial DTV. The radial gradients of these quantities are not linear proportional to the magnitude of the initial DTV.