A method and system for efficiently managing indoor air through cooperation between a mobile device and a stationary air conditioner. The system may include at least one stationary air conditioner and at least one mobile assistant device that move with a predetermined management area and cooperates with the air conditioner. The air conditioner may include an air quality improving unit improving a value of a predetermined air quality index into an appropriate range, a first forced flow unit generating a main flow to transport improved air toward the abnormal region, and a control unit controlling the air quality improving unit and the first forced flow unit to perform a main operation on the abnormal region and transmitting a command instructing the assistant device to perform an assistant operation on the abnormal region to the assistant device.