Abstract: The air thickness can effect the heat-insulation of the complex heat insulation wall. Though the contrast between the theoretical calculation and simulation calculation of the thermal insulation performance of vehicle multilayer composite structure，the influence of air layer inside the heat insulation wall is studied. The result shows that when the air thickness reaches a certain degree in the K’s analysis and calculation of the multilayer composite vehicle heat insulation wall，the influence of natural conversion on the thermal insulation performance of multilayer composite wall will be greater. In this paper，the methods of Polynomial Denisity and Boussinesq Model are used to verify the result.