Abstract: Microbicides have attracted much attention because they are environmentally friendly in use. In order to isolate the spore endophytic bacteria of arbuscular mycorrhizal fungal（AMF） from the rhizosphere soil of Paeonia suffruticosa ′Feng Dan′, the antibacterial activity of the obtained strains was evaluated by the plate standoff method, and the target strains were identified by polyphasic classification and verified by application effect of pot test. The results showed that six strains with antibacterial activity against Alternaria suffruticosae were obtained from the spores of soil arbuscular mycorrhizal fungi of Paeonia suffruticosa ′Feng Dan′ inter-rhizosphere, among which strain MB-12 had the best antibacterial effect with a plate inhibition diameter of 13.61 mm. It showed antibacterial effects on Fusarium oxysporum, F. graminearum, F. culmorum, Botrytis paeoniae and Cercospora paeoniae in various degrees and had a wide spectrum of fungal pathogenic inhibition. The results of the pot test showed that strain MB-12 could reduce the disease index of peony black spot and the biological control effect reached 71.25%. The results of biological activity test showed that this strain had the activity of secreting indole-3-acetic acid（IAA） and dissolving phosphorus, potassium and cellulase. During in vitro tests, strain MB-12 can grow at pH 4～10, 7.5% NaCl and 30% PEG. It can tolerate moderate drought and had good ecological adaptability. According to the results of morphological, physiological, biochemical, and molecular biology multiphase assay, strain MB-12 was more closely related to Microbacterium oxydans and belonged to Microbacterium. MB-12 can be used as a backup strain for black spot of peony biocontrol and growth-promoting agent development, with promising developmental applications.