Abstract: To clarify the bio-control effects of Piriformospora indica on target spot diseases for tobacco, the resistance effect and physiological mechanism of P. indica against target spot diseases and the influence on tobacco growth were studied by plate confrontation assay, mixed fungus and pot inoculation methods. The results showed that the colony size and growth time of P. indica were linearly correlated with the pathogen of tobacco target spot (Rhizoctonia solani), and the growth rate of P. indica was significantly lower than that of R. solani. R. solani could not grow normally on the mixed fungal medium. After 20 days of irrigation with P. indica broth, P. indica was able to colonize tobacco roots. The target spot size was significantly inhibited when P. indica was colonized on tobacco roots prior to inoculation with R. solani. The resistance mechanism to target spot disease was significantly correlated with decreased malondialdehyde (MDA) content and increased activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL) and proline (Pro) content. Chlorophyll content, plant height and the fresh weight, dry weight, length and width per leaf after irrigation with P. indica broth were significantly higher than those of the control group. P. indica can inhibit the normal growth of R. solani, improve the resistance of tobacco to target spot disease, and promote the growth of tobacco.