The invention belongs to the field of automobile air conditioners and particularly relates to an air conditioning system capable of detecting poisonous and harmful gas in air and automatically controlling and adjusting the air volume. The vehicle air conditioning system comprises an air inlet pipe, an air detection device, an air conveying device, an air inlet device, a filter device, a display device, a passenger detection device and a vehicle-mounted computer control device which is in data connection with the air detection device, the air conveying device, the air inlet device, the filter device, the display device and the passenger detection device, sends out a control instruction and further controls automatic switching between air inner circulation and outer circulation.