According to the identical border requirement of thermal loads in a chassis, the thermal-power consumption of electronic function modules and the heat flux density of a thermal runaway surface at thermal sta. bility state are analyzed and calculated. The integral thermal runaway characteristic is analyzed by calculating the hot flow density value which is from cooled natural convection air between the chassis and outside. And the re. sults are compared with the hot flow density threshold of air natural convection thermal runaway. Based on this, the simulation of CAD numerical sample is completed by simulation software UG NX7.5. CFD and thermal simu. lation analysis are performed by thermal simulation analysis software of ANSYS Icepak limited elements. Param. eters assumption and grids plotting of the chassis are completed. Accurate calculations of thermal simulations are performed to validate the thermal design reliability of the chassis and provide references for thermal simulation analysis and thermal runaway optimum design of other similar electronic equipment.