There will be 70 million tourists during Shanghai World Expo and there will be 0.8 million tourists in highest peak days of tourists.Therefore the Shanghai World Expo must harm Shanghai environmental quality.Urban environmental carrying capacity was studied during Shanghai World Expo in this paper.The results showed that the bad effect on urban environment would be vehicles tail gas and noise in highest peak days of tourists.But so long as the traffic mode was controlled in orbit traffic making up fifty-two percent of total traffic,buses thirty percent,cars seven percent,ships six percent,going slow five percent,Shanghai air environment could carry the pressure from vehicles tail gas.So long as the noise was controlled,it could be reduced under national standard,for example paving reduced noise,limiting vehicle speed,prohibiting sounded horn,discarding bad vehicle or installing silencer,and so on.