Abstract: Wheel polygonal wear of a high-speed train is an uneven wear along the wheel circumference, which is one of the common wheel failure phenomenon during trains operation. It could generate severe wheel-rail interactions that seriously threaten the structural safety and operation reliability of the vehicle system. As a core component to ensure the running safety of high-speed trains, the interface tribological behaviour of the brake system is directly affected by the wheel-rail interactions. Thus, the tribological behaviour of the brake system is extremely complex during braking process with the internal disc-pad frictions and external wheel-rail interactions. To investigate the braking interface tribological behaviour of a high-speed train excited by wheel polygonal wear, a rigid-flexible coupled vehicle dynamics model and a thermal-mechanical coupled finite element model of the brake system were established. Besides, the accuracy of the vehicle coupled dynamics model and the thermal-mechanical coupled finite element model was verified by field experimental test and bench test. Then, a braking interface tribological behaviour analysis method considering wheel polygonal excitation was proposed, which reflected the braking interface tribological behaviour during vehicle operation. In the proposed analysis method, both of the external wheel-rail interactions and internal disc-pad frictions were considered. The wheel-rail interactions were integrated into the method through vehicle dynamics model using the vibration and dynamic forces. Moreover, the measured data of wheel polygonal wear in the field experimental tests was employed in the method to reveal the wheel-rail excitations and braking interface tribological behaviour more realistic. On this basis, the effects of wheel polygonal wear excitation on the tribological behaviour of the brake system from the viewpoint of dynamic contact, temperature and vibration characteristics at different vehicle operating speeds were investigated in detail. The results showed that the wheel polygonal wear led to more complex and intense tribological behaviour of the system in terms of contact area, frictional heat, contact pressure and vibration. In addition, the standard deviation of the contact area and the root mean square value of the vibration acceleration increased with increasing speed. Compared with normal wheels, when the vehicle running speed increased from 50 to 300 km/h, the measured wheel polygonal wear contributed to an increase of 99.7%, 92.8%, 72.3% and 163.7% in the root mean square value of the brake system vibration acceleration, respectively. Therefore, wheel polygonal wear had a non-negligible effect on the tribological behaviour of the braking interface. The research results provided an effective method and engineering guidance for the study of the interface tribological behaviour and the structure design optimization of the brake system. Besides, the proposed models and braking interface tribological behaviour analysis method can be further applied to dynamical and tribological behaviour related assessment of bake system excited by other complex wheel-rail excitations.