The heat dissipation of a ventilated disc on high-speed trains during emergency braking is studied to improve heat dissipation performance. The conjugate heat transfer method is employed to understand the distribution and variation of convective heat transfer coefficients on the disc surfaces during braking. Finite element models of the ventilated disc and the complicated air flow field under the train are built. Boundary conditions are derived based on real working conditions. Heat transfer simulation is carried out using the FLUENT computer code. Simulation results, including temperature rise of the disc, convective heat transfer coefficient distribution, and heat transfer rate, are presented and analyzed. Using materials with high thermal conductivity coefficients and reducing the heat transfer wall thickness of the disc are proposed to improve the heat dissipation performance of the disc based on the simulation results. Both methods are effective in improving the heat transfer rate of the disc with a 10% improvement in the improved thermal conductivity case and a 30% improvement in the reduced wall thickness case.