An intelligent control method used in an intelligent control system includes an intelligent control device and an air condition device. The intelligent control device records CO2 amount value in an area continuously after the air condition device is started, and calculates a CO2 reference value based on the recorded CO2 amount value after a luminaire device in the area is turned off. Then, the intelligent control device records the CO2 amount value for a time period and calculates a CO2 compared value after the time period passes. The intelligent control device determines whether the CO2 amount value trend is varied upwardly or downwardly for choosing among keeping the current state, switching the operating mode of the air condition device or turning off the air condition device.