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The climatic factors influencing the occurrence of citrus yellow shoot trees are studied by using the climatic data of the Congjang Meteorological Bureau (the daytoday temperature, precipitation, evaporation and number of consecutive rainy days) from May to October, 1981 to 2005. The results indicate that when the tenday average temperatures in three dekads in summer (the third dekad of May, the first and second dekads of June) surpass 27 ℃, the tenday average differences between precipitation and evaporation are positive from middle May to end of June, and the number of consecutive rainy days is greater than five, the citrus yellow shoot is likely to occur. Therefore, the high temperature and humidity from the end of spring to the beginning of summer is the important condition for the occurrence of citrus yellow shoot for citrus tree tops.