Abstract: With the increase of running speed, the external disturbance of high speed EMU becomes more and more severe. In particular, when the EMUs pass through the tunnel and meet in the tunnel, the violent transient pressure generated by the external surface of the EMU is transmitted into the compartment, which will cause ear discomfort to drivers and passengers. Aiming at studying the influence of the airtight performance of EMU during operation on the pressure fluctuation and the passengers ride comfort, this article adopted the analysis method with combination of the dynamic and static test, combining with the time constant model and the equivalent leakage area model, through the internal and external arrangement of air pressure fluctuation monitoring sensors in different vehicles, carried out the aerodynamic load test before and after the operation of the EMU maintenance (Level IV) . According to the specific structural characteristics of different parts, different types of gas leakage testing equipment were developed to test and study static air tightness of different vehicles. The dynamic and static hermetic performance analysis model was established and the related air indexes were obtained, then the influence law of the condition of tunnel, speed and other factors on the interior pressure fluctuation and dynamic airtight performance was summarized. At the same time the leakage and the leakage area of the typical air tight parts were analyzed, and the effect of air sensitive parts sorting and optimized scheme were put forward. The method and relevant research data proposed in this paper have certain reference significance for the design scheme and repair program optimization of key components.