The invention discloses hydrangea polysaccharide and its application in treating myocardial ischemia-reperfusion injury. The invention provides a hydrangea polysaccharide, which is prepared by the following method: collecting hydrangea macrophylla leaves, washing, drying in the shade, pulverizing, extracting with deionized water under hot reflux, filtering, concentrating the filtrate under reduced pressure, and centrifuging to collect the supernatant, Add three times the volume of absolute ethanol, mix well, let stand for alcohol analysis, collect the precipitate, redissolve with deionized water, repeat the same method of centrifugation, alcohol precipitation once, collect the precipitate, wash with absolute ethanol and acetone, and deionized water Reconstituted, deproteinized by Sevag method, and freeze-dried. Pretreatment with the hydrangea polysaccharide can effectively reduce myocardial ischemia-reperfusion injury in rats, and its mechanism of action is related to reducing myocardial cell apoptosis in ischemia-reperfusion rats, and can be used to prepare drugs for antagonizing myocardial ischemia-reperfusion injury .