By way of analyzing the frictional contact status of the drum brake and taking the temperature model of frictional coefficient into account, the thermo-mechanical coupling numerical simulation of the established 3D finite element model for the rear wheel’s drum brake of commercial vehicle EQ1208 is carried out for the inertia brake operation. Then the simulation results of coupling transient temperature field of the drum brake are obtained. Though the A point temperature-rising results comparison between test and simulation, the variation trends of them are coordinate and the simulation results are accurate. It is indicated that the 3D thermo-mechanical finite element model are fit well. At last the main influence elements（vehicle velocity and road grade）of the brake temperature rising for the inertia brake operation are analyzed. 