Abstract: 【Objective】To analyze effects of tobacco root black rot incidence degree on soil nutrients and microbial community structure,to explore relationship between soil environment and microbial community under different disease occurrence conditions,so as to provide a theoretical basis for prevention and control of black root rot.【Method】Tobaccogrowing area of Anshun,Guizhou was investigated. Rhizosphere soil of different incidence degrees of black rot(grade 0,1,3,5)was collected to determine physical and chemical property of the soil. 16S rDNA and ITS high-throughput sequencing technology were used for sequencing analysis to explore the differences in rhizosphere soil nutrients,bacterial and fungal community structure of tobacco plants under different disease degrees.【Result】Compared to normal soil,the severer the disease,the lower the evenness and richness of soil bacterial community and the higher the evenness and richness of soil fungal community. Compared with normal soil,relative abundance of bacterial communities Sphingomonas,Candidatus_Udaeobacter,Bryobacter,and Gemmatimonas in the pathogenic soil decreased;and abundance of Bacillus increased;abundance of fungal communities Fusarium,Cylindrocarpon,Mucor decreased and abundance of Nicotiana,Setophorna,Thanatephorus,Coniochaeta,Plectosphaerella,and Tetracladium increased. Analysis of the indicated species showed Gemmatimonas,Plectosphaerella,Tetracladium were the main different species in soil bacterial and fungal communities of difference incidence degrees at genus level.Resultsof redundancy analysis(RDA)and variance decomposition analysis(VPA)showed that soil ammonium nitrogen(NH-N)and soil organic matter(SOM)were the main driving factors for changes in bacterial and fungal community structure.【Conclusion】Abundance decrease of bacterial Gemmatimonas and abundance increase of fungal Tetracladium are the key microbial factors for the serious occurrence of black rot in tobacco root,and increasing soil SOM and NH-N content can effectively reduce the incidence of tobacco root black rot.