Thermal design is to use proper cooling technology and structural design for components of producing heat and whole machine, to control the temperature field of the whole machine. Heat dissipation of the cabinet can be divided into natural convection and forced ventilation. Natural cooling design is to bring forward a reasonable thermal design for open-type or close-type cabinet by selection the space between printed circuit boards and calculation of heat exchange of convection. The forced ventilation design is to realize reasonable control and distribution of the airflow by selecting blower fan and designing air channel.