The boundary layer of the air flow blowing the surfaces of the brake mechanism prevents heat transfer from heated surfaces. The obtained analytical dependences of the velocities` and temperatures` distribution in the boundary layer represent the field of the boundary layer as a multilayer structural model, the laws of change in the velocities and temperatures of the air flow blowing depend on various sub layers of the boundary layer. According to these analytical dependencies, a thermal model “ventilated brake disc - external condition” was developed. The thicknesses of the boundary layers of the air flow blowing on the various surfaces of the brake disc are determined by various processes. For the working surfaces of the brake disc, the determining criterion is the thickness of the diffusion layer, while for the surfaces of the ventilation apparatus, the criterion for estimating the thickness of the boundary layer is thermal processes. In future, the developed thermal model “ventilated brake disc – external condition” should be the basis for thermal calculations in designing disc-shoe type brake mechanisms.