An air detection system is provided and includes an intelligent device and an internet of things processing device. The intelligent device includes an inlet, an outlet, a gas-flowing channel, a control module and a gas detection module. The gas-flowing channel is disposed between the inlet and the outlet. The control module is disposed in the intelligent device and includes a processor and a transmission unit. The gas detection module is disposed in the gas-flowing channel and electrically connected to the control module. The gas detection module includes a piezoelectric actuator and at least one sensor. The piezoelectric actuator inhales gas into the gas-flowing channel through the inlet and discharges the gas through the outlet. The sensor detects the introduced gas to obtain gas information and transmits the gas information to the control module. The internet of things processing device is connected to the transmission unit of the intelligent device for receiving the gas information.