The present paper dealt with the effect of the avirulent strain RS-1403 of Ralstonia solanacearum on the ecological characteristics of microorganism fatty acids in the rhizosphere of tobacco. The tobacco plants were treated with the avirulent strain RS-1403 in the concentration of 1.0×10⁶ cfu/mL with water as control in the semi experiments. The rhizosphere soil was sampled at different days etc. 5d, 10d, 15d, 20d and 25d after treatment. The phospholipid fatty acids (PLFAs) of the soil samples were detected by.GC of Agilent6890N. Pattern, content and structure of the microbial PLFAs in tobacco rhizosphere soil were evaluated and the difference between treatment and water control were compared to analyze the immune disease-resistant mechanism of the strain RS-1403 against tobacco bacterial wilt disease at the microbial community level. The results showed that the microbial PLFAs pattern and content in the tobacco rhizosphere soil were changed under the stress of the avirulent strain RS-1403. The fluctuation of microbial PLFAs could be divided five types, e.g. declining type, unchanging type, <50% increasing type, 50%-100% increasing type, and >100% increasing type. Among which, the reduction of 10Me16∶0 indicative to actinomycetes represented the decreasing type, all of the PLFAs in >100% increasing type indicated to G^- bacteria. The statistical analysis showed that the inoculation of RS-1403 could change the microbial community structure in the tobacco rhizosphere soil due to improving the growth of bacteria and fungi and inhibiting the reproduction of actinomycetes. Inoculation of the stain RS-1403 could increase the microbial community diversity in the soil, in which, the enhancement of SHANNON index of community dominance, Simpson index of community abundance and Pielou index of uniformity was revealed. The differentiation of microbial sub-community in the tobacco rhizosphere soil under the stress of the strain RS-1403 was also evaluated with cluster analysis. The results displayed the significant difference existed between RS-1403 treatment and water control. The rhizosphere soil microbe both in treatment and control could be divided into four sub-communities at 2.56 Lance-distance, which were different in the constitutes and characters of PLFAs. The tobacco rhizosphere soils in the RS-1403 threatening treatment and water control could be mainly clustered in to two different groups by using cluster analysis, it was clear that the RS-1403 could alter remarkably microbial community structure in the rhizosphere soil of tobacco.