Abstract: The passenger cabin of a high-speed train is relatively well-sealed. Thus the spreading characteristic of air pollutants within the cabin may vary significantly under operation due to the influence of different ventilation modes as well as the cabin layout structure. The present work conducted a systematic experimental study on the air pollutant spreading characteristic in the passenger cabin of a real high-speed train with a complete air condition system, wind passage structures and cabin decorations. The results indicate that, the air pollutants emerged in the middle of the passenger cabin can spread to both ends of the cabin, resulting in the increase of pollutant concentration to different levels at different locations. Particularly, the downstream can reach the highest pollutant concentration. The top air supply mode works better in restricting the air pollutant spreading than the bottom air supply mode. Two air purification techniques, i.e., intense field dielectric (IFD) and dielectric barrier discharge (DBD), can significantly increase the purification effect of air pollutants, and the effectiveness of air purification is positively correlated with the air pollutant concentration. Moreover, the IFD technique exhibits a better purification efficiency than that of the DBD technique.