The diagnostic experiment of the influences of different ventilated time and CO_2 concentra-tion on winter wheat are made by using the OTC -1 open top chamber. The results show that the influ-ences of CO_2 increase on the winter wheat development, grain yield and product quality are remarkablepositive effects no matter long or short the ventilated time. When the CO_2 concentration (700ppm) isthe sarne . the influences of 7 hours ventilated experiment on winter wheat development and yield forma-tion and other factors has an activation on physiological mechanisrn. The activation would be disap-peared with the ventilated time prolonged.