A strain SY-15 with high antioxidant activity was screened from 11 strains of endophytic penicillium.The fermentation broth was subjected to suction filtration,extraction,concentration,column chromatography and HPLC using activity tracking method.After separation,a compound was obtained,and it was found to be a polyketone by NMR analysis and comparative literature,containing the mother core of xanthone.The total antioxidant activity of the substance is 70.66 U/mL,the DPPH free radical scavenging rate is 80.67%,and the absorbance value of potassium ferricyanide is 1.43,which reaches 72.99%,81.76%,58.85% of the same concentration of vitamin C.In vivo experiments have shown that this compound can effectively improve the viability of yeast cells under oxidative stress,and has a certain protective effect on yeast cells against oxidative damage.