Abstract: The thermal environment of a solid rocket tail cabin was studied. There is obvious difference between the conditions in the sky and on the ground. The mechanism of convection thermal environment was analyzed by numerical simulation. In the real launch, there is a shear layer between the shock waves from the outflow of rocket tail cabin and fram the engine jet. The shear layer is connected with the tail cabin. An unsteady vortex structure is formed by the shock wave and shear layer, which is the source of convection heat flux in the tail cabin. The strength of shear layer is related to the convection heat flux. According to the mechanism of convection heat flux, a structural form of reducing convection heat flux was calculated. By weakening the shear layer at the rocket tail, the convection heat flux is greatly reduced. The thermal environment of solid rocket tail cabin is obviously ameliorated.