Abstract: Based on dynamic rule of sugar beet Cercospora leaf spot (CLS) occurrence time, the period of CLS chemical control is determined to provide a theoretical basis for the scientific management of CLS. From 2016 to 2017, the author used the method of field survey, to study the dynamic rule of CLS disease index and occurrence time. The results showed that the disease development time curve had four peaks in 2016, which were July 25, August 24, September 3 and September 18, and their disease indexes were 9.33, 42.5, 55.92 and 61.46, respectively. In 2017, the disease development time curve showed that August 14, August 19, August 24 and August 29 were four high points up to September 3, which was the first peak day of disease development, and disease indexes were 7.86, 10.75, 30.56, 36.53 and 42.88, respectively. At the early stage of disease (early and middle of July), rainfall was the determining factor of CLS spreading. The first fastigium and before rising point is the best time to spray fungicides, the time for spraying fungicides should be before July 25 in 2016 and before August 14 in 2017.