Abstract: The optimum application rate of tianyuan living-bacteria solution on flue-cured tobacco growth was investigated by large scale field experiments. The result showed that the decomposition of organic matter in composting accelerated after application of microbial agents. Application of 1 000 mL/667m2 microbial agents could increase the soil available K content by 125.00%. 500 mL/667m2 enhanced contents of available nitrogen by 91.61% and available P by 121.62% in soil. The soil density decreased and the degree of soil maturation was accelerated. Application of 2000 mL/667m2 microbial agents could decrease the soil density by 12.31%. Application of 1 000 mL/667m2 microbial agents could extremely increase weight of dry root 73.61%. By applying 1 000 mL/667m2 microbial agents, the indices of yield per 667 m2, production value, mean price and first-class tobacco leaves proportion increased to 26.32%, 59.33%, 26.59% and 5.66%, respectively. The score of aroma quantity and quality increased. The availability of tobacco leaf enhanced. In conclusion, application of 1 000 mL/667m2 microbial agents was the optimized volume to flue-cured tobacco production.