Types of thermal transmission in chassis for one special electronic equipment are analyzed. Steady thermal simulation is performed by professional thermal analysis software Icepak. To calculate the temperature field when the blocked structure getting heat equilibrium, reasons that the temperature of inner devices is above upper limited temperature are explained. Two methods for improving structures are proposed. Temperature field in chassis with vent holes on front and back panels for heat exhaust is calculated again. Calculation results show that the highest temperature in inner devices is in permitted operation temperature range. So the temperature in chassis is reduced effectively to ensure the equipments in stable and reliable operation states. And structure design and improvement effectiveness are enhanced.