Abstract: Experiments were carried out in a sunlight greenhouse in Daxing district，Beijing. The cucumber was cultivated by the cultural practices.Air temperature and relative humidity during the growing season（2012.10 to 2013.04）were collected.Based on the proper air temperature，relative humidity and leaf wet duration for disease infection，the probability of potential diseases were analyzed.The results showed that 88.1% potential diseases occurred in night and early in the morning.The managements during the period played a key role.The potential disease occurred days accounted for 22.8% during the experiment.97.7% potential diseases occurred from February to April.The most serious month was March，which accounted for 53.3% of the total.The vegetables from the sunlight greenhouse in March might be in the highest risk in food security.The conclusions could provide valuable information on crop disease management in greenhouse.

Key words: Temperature, Relative humidity, Leaf wet duration, Potential disease