Abstract: This paper studied the infection methods and parts， infection period， infection conditions and interactive pathogenicity of Rhizoctonia solani isolated from tabacco. The results showed that wound was beneficial for the infection of R.solani. The tobacco leaf， leaf vein， each part of stem and roots could be infected by the pathogen. Pathogen- infecting favorable stage of tobacco plant was seedling stage， and the disease rate under non-wound inoculation condition reduced significantly with the the growth of tobacco plant. At 25℃-30℃， the pathogen infection was strong， and the pathogen could not infect tobacco under 15℃. With the decrease of soil moisture in the range of 47.83%-76.41%， the disease index would increase. The results of modified selective medium testing showed that the higher the amount of soil pathogens had， the severer the disease occured. Interactive pathogenicity test indicated that R.solani isolated from tabacco could infect rice and corn， and R.solani isolated from rice and corn also could cause the occurrence of tobacco damping-off.