Thermo-mechanical coupled systems are typically complex, however, the demand for analyses of this kind of multi-physics system is increasing, for example, accurately predicting the temperature and thermal stress of the railway disc brakes. However, many models ignore the phenomenon of thermal expansion and wear on brake pads. Therefore, their influence on the result is unclear. This research aims to investigate the effect of these two phenomena on the temperatures and stresses. These influences represent different heat flux input methods. Based on the finite element method (FEM), a three-dimensional (3D) transient thermo-mechanical model is built up. Three cases with or without thermal expansion and wear are conducted. The model is validated against measurement data. Simulation results show that thermal expansion and wear on the brake pads cause a 10% difference in the average temperatures of the brake discs, while a 257% difference in the maximum temperatures. As for the equivalent stresses (Von Mises stress), the difference can reach 3500%. Overall, this research builds a thermo-mechanical model and quantifies the effects of thermal expansion and wear on the temperatures and stresses of railway brake discs. The model can be transferred to other thermo-mechanical coupled multi-physics systems.