Abstract: Using Honghuadajinyuan (Nicotina tobaccum L.cv.) , an experimentation by adding a microbial agent to the soil for 5consecutive years to determine the rhizospheric and economic effects on the tobaccos was conducted.The results showed that the treatment benefited the plant growth in general.It increased the yield, value and proportion of high quality tobacco.To some extent, the agent also alleviated the problems normally associated with the consecutive monoculture.The possible mechanism was, therefore, studied.The agar plate counts on the rhizospheric bacteria, actinomycetes and fungi in the soil were compared with the control to be higher by 128.57%, 191.43%, and 107.61%, respectively.BIOLOG analysis indicated that the average well color development (AWCD) of carbohydrates, phenolic acid, amino acids, amines and carboxylic acid were higher with the treatment than CK.Furthermore, the diversity indices on the microbes utilizing carbon sources, such as Simpson (J) , Shannon index (H) , Shannon index (H) evenness index, Brillouin index and McIntosh index (Dmc) , suggested a robust microbial functional diversity existed in the rhizospheric soil of the flue-cured tobaccos with the treatment.Among the soil enzymes, the polyphenol oxidase, urease and dehydrogenase all showed significantly higher activities than those of CK by 52.4%, 482.2%, 16.3%, 203.3% and 166.3%, respectively.The activities of polyphenol oxidase and dehydrogenase all reached an extremely significant difference level.It was, therefore, concluded that the addition of the microbial agent could ameliorate the micro-ecological system and the rhizospheric nutrient equilibrium of the soil promote the growth, yield and quality of the tobaccos.