Objective To evaluate the air quality in the long-distance bus with air conditioner and the uncomfortable index of the passengers during the trip. Methods The air quality in the long-distance buses with air conditioner which were running for 3 hours,5 hours,7 hours respectively was monitored and 200 passengers were investigated by questionnaire during the trip,Jan 2004 -Aug 2005. Results As the running time increasing,CO2 concentration significantly increased. The bacterium,fungus,PM10 and wind speed were increasing gradually,but still in the normal level. The temperature,CO,formaldehyde,benzene,toluene and dimethyl benzene did not increase. The hemolysis streptococcus was not found,the relative humidity droped a little but in normal level. The investigation results of questionnaire showed that 21.5%(43/200) passengers felt peculiar smell,64.5% (129/200)of them appeared lassitude symptom,43% (86/200)of them appeared the symptom of dizzy,thirsty and sore throat,21%(42/200)of them felt eye dry,14.5%(29/200)of them appeared the symptom of headache and breath-block,7%(14/200)of them felt nauseated and skin itch during the trip. Conclusion The CO2 pollution in the investigated long-distance buses is serious and this can impact the health of the passengers.