Abstract: To improve the gaseous micro-environment for plantlet in vitro and decrease the cost, based on controlling CO₂ concentration by gas flux and by gas pressure, a new comprehensive auto-control system of gaseous micro-environment was developed. By using this system the control experiment with the Ipomoea batatas(L.) lam plantlets was done. Aaccording to the related literature, the light density, the CO₂ concentration and the relative humidity were selected as 250 μL·m^-2·s^-1, 8750 μL·L^-1 and 75%～85%, respectively. And the results show that the system was able to work reliably and steadily, to promote photosynthetic ability of plantlet and improve their physiological and biochemical indexes.