Abstract：In order to explore the interaction mechanism of‘ biocontrol bacteria-Phytophthora-pepper root system’，this study took Paenibacillus polymyxa LRS-1 as biocontrol material；applied pot experiment in greenhouse；detected the composition and types of pepper root exudate under Phytophthora stress．The result showed that compared with the negative contrast，the contents of organic acid，protein and soluble sugar in pepper root exudate under Phytophthora stress were significantly increased，and the contents of organic acid and soluble sugar under Phytophthora stress and inoculated with Paenibacillus polymyxa LRS-1 were significantly decreased，while the protein content was significantly increased．The main components of pepper root exudate were esters，acids，amines，alcohols，ketones and hydrocarbon compound identified by GC-MS．There were more esters，acids and amines with relatively complicated structure，and less hydrocarbon and alcohol compound dominated by straight-chain or branched-chain alkanes．Under Phytophthora stress，the compound kinds in pepper root exudate increased significantly，and specific compound elements including methyl palmitate,etc. were detected．While，under Phytophthora stress，the compound kinds and contents in pepper root exudate inoculated with Paenibacillus polymyxis LRS-1 tended to be the same as the negative contrast．In addition，the relative contents of 3-phenyl-2-methyl acrylate，etc. in root exudate of pepper inoculated with LRS-1 was the highest，verifying that inoculation of Paenibacillus polymyxis LRS-1 could obviously alleviate the stress from Phytophthora infestation on pepper roots allelopathic．
