Abstract: Irrigating roots of tobacco plants with soymilk (made from traditional soybeans and fermented soybeans) is a topdressing technology used in some local tobacco-growing conservation areas in China. To study the influences of root irrigation with soymilk on the growth of flue-cured tobacco, soil nutrient contents, agronomic traits and root growth of tobacco plants and soil bacterial community structure were investigated by both pot and field experiments. The results showed that the contents of soil protein and labile organic carbon increased significantly in the early stage of soymilk root irrigation, and the contents of soil nutrients such as alkali-hydrolyzed nitrogen, available phosphorus and available potassium remained relatively high in the middle and late stages of root irrigation. The growth of flue-cured tobacco roots and leaves were promoted by the treatment. At the early stage of the root irrigation, the number of bacteria increased rapidly, and the abundances of dominant bacteria in soil varied significantly among the different treatments. However, there was no significant difference among the abundances of dominant bacteria in the middle and late stages of the irrigation. At the early stage of the root irrigation, the relative abundances of various soil functional bacteria involved in nutrient cycling, the secretion of plant growth regulators, and the inhibition of pathogens increased significantly. Therefore, this irrigation technique appeared to improve the yield and quality of flue-cured tobacco by increasing soil nutrient contents, raising the relative abundances of beneficial functional bacteria, improving soil micro-ecological environment, and promote the growth of roots and leaves of flue-cured tobacco.