Abstract: In view of the characteristics of high train running speed and high operating line tunnel blocking ratio of city railway, in order to effectively prevent the external air pressure fluctuation that changes drastically from entering train, based on the brief description of the interior air pressure fluctuation control index and the air pressure fluctuation control mode of high-speed EMU, the overall air-tightness control index of city railway train is proposed. The composition, working principle and control mode of two kinds of passive pressure protection systems for city railway train are studied. In-vehicle test results show that both the interior air pressure fluctuation control schemes can meet the requirement of maximum air pressure change of less than 800 Pa within 3 seconds, and the control effect is good. In addition, the interior air pressure fluctuation is tested under both the fully open and fully closed states of fresh air electric volume regulating valve. Test results show that the maximum pressure change within 3 seconds can be reduced by 10% under the fully closed state of fresh air electric regulating valve.