On the basis of the environmental characteristics of whole-closed air-conditioned coaches，the parameters of air temperature．relative humidity，air velocity，the volumetric concentration of CO，C02，formaldehyde and the fresh air auantity are selected as typical objective assessment indexes．The subjective investigation table is designed according t0 the general international rules．Subjective and objective assessments of the air quality in whole-closed air-conditioned e0aches．which run from Guangzhou to Shenzhen，were made．Based on th

grey characteristics of the air cruality in the coaches and the assessments，the relationship between the 0bjective index，es and the passengers subjective feeling was analyzed by using the grey system incidence theory．The result~’§h that the key objective indexes．which affect the air quality in coaches，are the quantity of fresh air，the concentration of CO2 and air ternperature