The invention relates to a medicine for preventing and treating a stroke, especially an ischemia stroke. The condition that the medicine has prevention and treatment effects on the stroke, especially the ischemia stroke is verified through researching and analyzing the structure characteristics of a coumarin derivative as shown in a formula I and researching the pharmacodynamic characteristics of the coumarin derivative in rats. In addition, the coumarin derivative as shown in the formula I shows good curative property in a cerebral ischemia reperfusion test of a mice, the behavior score of the cerebral ischemia reperfusion mice can be significantly reduced, the edema degree and the moisture content of injured brain tissue can be reduced, the cerebral infarction ratio is reduced, and the medicine can be used for preventing and treating the stroke, especially the ischemia stroke.