Abstract: In order to investigate the inhibition mechanism of Bacillus megaterium LB01 against Colletotrichum gloeosporioide in postharvest mangos,fruit acupuncture and fungistasis.in vitro were used to measure the inhibitory activity of fermentation filtrate of Bacillus megaterium LB01,then DCFH-DA,spectrophotometry,MitoTracker Red CMTMRos and PI probe were utilized to study the effect of Bacillus megaterium LB01 fermentation filtrate on ROS level,MDA content,mitochondrial distribution and membrane integrity of conidia. It was found that the fermentation filtrate of Bacillus megaterium LB01 could significantly inhibit the incidence of postharvest mangos and the extension of lesion.. The results of ROS stained in conidia by DCFH-DA showed that the staining rates of conidia treated by LB01 fermentation filtrate were 73.24% and 84.31% respectively after 6 and 12 of culture,while the control values were only 65.25% and 72.23% respectively. The results of the absorbance test of the reaction products of MDA-TBA showed that the MDA contents of the treatment group was as high as 0.78 nmol/mg after 6 h of culture,while the value of the control group was only 0.62 nmol/mg after 12 h of culture. The MDA contents of the treatment group increased significantly,indicating that the inside of the cells had been severely oxidized by ROS. In addition,the results of MitoTracker Red CMTMRos and PI staining showed that mitochondria was significantly damaged and the integrity of cell membrane was seriously destroyed. Therefore,the inhibitory mechanism of Bacillus megaterium LB01 was to achieve the antifungal effect by inducing ROS level,MDA contents,damage mitochondria,and destroy the integrity of cell membrane,which could lay foundation for further study on the biocontrolling mechanism against postharvest mango anthracnose disease