Abstract: Yunnan is a major tobacco-producing area, because large-scale cultivation of a single species and unreasonable fertilizers application, result serious tobacco diseases, which restricts the quality and income of flue-cured tobacco. nitrogen, potassium concentrations and nitrogen and potassium balance in tobacco middle leaves and anthracnose, brown spot diseases were investigated in the center of Yunnan province at the vigorous growing stage .Results showed that: (1) Nitrogen concentrations of flue-cured tobacco were relatively high, and potassium concentrations were low , resulting nitrogen / potassium ration more high. (2) when nitrogen concentrations>4%, too much or too little potassium concentrations, disease indexes were increased. (3) when nitrogen and potassium concentrations were in normal range, tobacco plant had the strongest resistance to diseases. (4) when nitrogen / potassium ration >2%, the resistant of tobacco to diseases were reduced , with nitrogen / potassium ration deviation from the optimum level, disease indexes of tobacco anthracnose and brown spot were increased.