Abstract: In order to study the antibacterial activity of oleander fresh leaves flavonoids on rice blight and the mechanism of action on the cell wall and cell membrane of rice blight,different concentrations of oleander fresh leaves flavonoids were used to treat rice blight fungus to study their effects on the mycelium of rice blight bacteria.The results showed that the minimum inhibitory concentration of oleander fresh leaves flavonoids against blight blight was 4 g·L^-1.The scanning electron microscopy results showed that the thickness of the untreated hyphae’s thickness was uniform,the surface of the hyphae was smooth and full,and the stretch was good.After the treatment of oleander fresh leaves flavonoids,the hyphae were seriously damaged,the folds were obvious,the inner concave holes were deepened,the cells were ruptured.The activities of chitinase andβ-1,3 glucan enzyme were significantly induced.Flavonoids from fresh leaves of Nerium significantly affect the permeability of cell membrane of Rhizoctonia solani,and a large amount of cell contents were released,which improved the permeability of the cell membrane of pathogenic bacteria and inhibited the synthesis of ergosterol,the structural substance of the membrane,and the longer the action time,the more destructive it was.In summary,it affects its normal physiological function and provides new ideas for effectively preventing rice sheath blight.