Growth speed of Oyster mushroom buds is connected with several factors, ventilation is one of them. In general case, there is no major impact occurred on bud growth of Oyster mushroom provided that concentration of carbon dioxide is not higher than 0.5%, but once it reaches at or above 1%, bud growth would be seriously inhibited, which brings about malformed mushrooms. In actual production, it is proper for cultivators to control the concentration of carbon dioxide at about 0.05% so that optimal level could be satisfied.