Abstract: The long-term use of metiram（with the application concentration of 104 mg·L⁻¹ ）against tobacco brown spot disease in Chuxiong tobacco-growing area has caused excessive pesticide residues in tobacco leaves. To reduce the effect of metiram on tobacco leaves, this study used 104 mg·L⁻¹ as control to investigate the efficacy of 3 reduced concentrations（84 mg·L⁻¹, 64 mg·L⁻¹ and 44 mg·L⁻¹）of metiram on mycelial growth of Alternaria alternata MD-YX-Z1and A. tenuissima YA-QL-B2（the two main pathogens responsible for tobacco brown spot in Chuxiong tobacco-growing area). Then pot experiments and field experiments carried out with the same concentrations of metiram to investigate the control efficacy against tobacco brown spot disease. The results showed that the reduced 3 concentrations of metiram all can inhibit the mycelial growth of the two Alternaria species while the concentration of 84 mg·L⁻¹ with a better inhibition rate. Pot experiments and field experiments also confirmed the reduced 3 concentrations of metiram can control tobacco brown spot disease while the concentration of 84 mg·L⁻¹ with a better control efficacy. The concentration of 84 mg·L⁻¹ reduces approximately 19% in fungicide dosage compared with the field application dosage 104 mg·L⁻¹ and can mitigate the risk of pesticide residues.