This paper discusses how to improve thermal insulation performance through one or several effective methods when designing rail vehicles. These methods are all validated by simulation analysis and testing. The EMU (Electric Multiple Unit) train is selected as a basic model for thermal analysis. The vehicle is divided into several modules based on thermal insulation characteristics and different thermal insulation materials and applications are compared and analyzed. A design solution which could improve the overall thermal insulation performance of the vehicle is proposed. The vehicle structure is divided into modules on different levels, and the thermal insulation performance of each module is analyzed preliminarily. Based on the proportion of each module in the vehicle, its influence on the overall thermal insulation performance is evaluated. Typical modules include carbody underframe, side wall and roof. Based on the preliminary thermal analysis results of modules above, the typical models of each component are established for study, calculation, and testing. The thermal insulation coefficients of different areas are compared to determine which one has the most potential of thermal insulation improvement. Technical cost, material cost and manufacturability are comprehensively analyzed to figure out the most reasonable insulation solutions for each module. Then, the proportion of each module in the vehicle and overall costs of thermal insulation proposal are analyzed to identify the correlation between the structure of each module and improvement of vehicle level thermal insulation performance. The solution to effectively improve the thermal insulation is proposed from a decision matrix, which consists of importance of proportion, difficulty of realization and comprehensive cost. At last, the simulation analysis and test data of the overall vehicle heat insulation performance are compared to validate the consistency between theoretical analysis and practice, which could further prove that the design solution proposed in this paper is feasible and effective.