Abstract: To reveal natural occurrence of citrus liberobacter asiaticum and provide a scientific basis for monitoring, preventing and controlling the disease, a study was made from 2002 to 2015 on natural infection morbidity in a citrus orchard with good natural isolation barrier by taking three sample plots to find out the onset and diffusion of the disease. The fourteen-year study showed that citrus liberobacter asiaticum morbidity was the most powerful four or five years after the natural infection, and reached 10% to 15% yearly, which increased by two to three times compared with its early incidence force. Its varying curve of occurrence acted as an“M”. The first peak symptomatic appearance of natural infection was around the 5th year after the first incidence and the second happened 9 years later or so. Generally, the peak period lasted 1 to 3 years and the change between the two peaks fluctuated with high volatility. The occurrence regularity of citrus liberobacter asiaticum morbidity showed an upward trajectory in Logistic curve and its chronological value change model was: Q = 85.8144 1 EXP(4.0063-0.5837N ) (n=14，r=0.9941**), and its big cycle of natural infection spreading was 15 years (including core harm period of 10 years or so). This change patterns could be of guiding significance to monitoring, preventing and controlling citrus liberobacter asiaticum in old orchards.