Abstract: Thermal design is important in reliability design of component，equipment and system．In this paper，the thermal design at the level of cabinet and modules for a signal controlling and processing equipment is introduced．Forced convection is an usual cooling method．Airflow's routing and separating should be considered under the condition of using several fans in the cabinet．The thermal simulation is conducted with the software of Flotherm，not only to do the thermal analysis of the cabinet，but also to optimize the structure，which makes the structure more reasonable，the cooling more efficient，the equipment more reliable．