Abstract: Chlorophyll fluorescence and hydroxyl radical(·OH)content in ambient air were measured in banana seedlings growing in closed incubators in which light intensity,temperature,acidity and alkalinity were controlled.The correlation between changes in photosynthetic characters and ·OH content in ambient air was studied under different environmental conditions.Results showed that the level of ·OH was obviously higher in the incubator growing banana seedlings than in the incubators without growing plants,which indicated that the level of ·OH in ambient air could be improved by growing plants in it.Chlorophyll fluorescence parameters changed obviously under different culture conditions.Stronger light intensity,extreme cold and hot temperature,excessive acidity or alkalinity indicating different degrees of photo-inhibition in different culture conditions,suggesting a strong correlation between the level of photo-inhibition and ·OH content in ambient air.We also found that the level of ·OH increased with the degree of photo-inhibition.The affect of the plants on the level of ·OH was confirmed,and the strong correlation between the level of ·OH and the growth status of the plants was demonstrated.Further studies on the evolvement mechanism for ·OH in the atmosphere are recommended.