Abstract: In order to determine the periodic occurrences, biological characteristics and high effective fungicides of tobacco brown spot disease in Sichuan Province, systematic investigation was carried out to study the occurrence of brown spot of tobacco for three consecutive years in 5 major planting areas of Sichuan Province including Luzhou, Liangshan, Panzhihua, Guangyuan and Yibin. Tobacco samples with typical symptoms of brown spot were collected at maturity. To identify the causal species of the disease, colonies isolated from brown spot-infected tobacco were studied using macromorphology, micromorphology and molecular biology methods and growth rate and germination rate determined. At the same time, the screening of high efficiency emergency chemicals for brown spot of tobacco was conducted in tobacco fields. The results showed that the causal pathogens identified from tobacco samples with typical symptoms of brown spot from the 5 major planting areas of Sichuan Province were all Alternaria spp. There were no significant difference in colony diameter, spore production and germination rate among the isolates of Alternaria spp. on SDAY media. The disease index of Alternaria spp. increased gradually with time from the end of June to September every year in the 5 growing areas of tobacco. In August of every year, the disease index of Alternaria spp. in the 5 growing areas of tobacco was significantly higher than that in July and reached a peak. 10% Difenoconazole water dispersible granule and 40% mycelium net wettable powder had good control effects to control Alternaria spp of more than 60% which was stable among the 5 growing areas.