Abstract: To explore effects of mixed pesticide applications on control effects of tobacco brown spot and tobacco leaf quality, tobaccos in Ankang City, Shaanxi Province were selected as research object．Field positioning experiments were carried out by 4 pesticides and setting 9 application combinations．Results showed that the maximum tobacco leaf width was significantly higher than other treatments after 3% polymyxin water solution, Bacillus subtilis, 40% dimethachlone wettable powder, and triazolone were mixed in 1∶1∶1∶1．Application of 3% polymyxin water solution or triazolone alone improved tobacco yields and production value, with a higher rate of first class tobacco．Control effects under treatments with single application of 3% polymyxin water solution or 40% dimethachlone wettable powder alone on tobacco brown spot was better than treatments with mixed pesticide application．Tobacco leaf quality treated with no pesticide application was the best, followed by 3% polymyxin water solution alone．Tobacco leaf quality treated with Bacillus subtilis mixed with triazolone at a ratio of 1∶1 was the last．It indicated that mixed applications of pesticides would reduce control effects of tobacco brown spot disease and tobacco leaf quality．Theoretical supports was provided for prevention and control on tobacco brown spot disease and powdery mildew in tobacco growing areas of Southern Shaanxi．