The current thermal model of railway disc braking is rather coarse as the heat source is treated to be uniformly distributed. By using a Gaussian mixture function, the thermal behavior of railway disc braking was modeled. Simulations and full-scale rig tests of emergency braking about metro train at 40–100 km/h were conducted. The differences between the maximum temperatures calculated by the Gaussian mixture heat source method (GMHS method) and measurements are 2.56–4.71 °C. The relative errors between the maximum temperatures calculated by the GMHS method and thermal mechanical coupling method (TMC method) are no more than 2.53%. The temperature curves obtained by the GMHS method oscillate about their centerline with the same oscillating period to the TMC method. The time cost by the GMHS method is only 0.91–3.05% of the TMC method at the same conditions. The results indicate that the proposed GMHS method is accurate and efficient, which is more suitable for engineering application.