The invention relates to the technical field of medicines, in particular to application of 3,5,3',4'-trihydroxy stilbene-3'-O-beta-glucoside and a derivative thereof to the preparation of a drug for preventing and treating brain edema. The invention discovers through an experiment that the 3,5,3',4'-trihydroxy stilbene-3'-O-beta-glucoside can obviously reduce the cerebral water content in four models of mice, namely a mouse focal permanent cerebral ischemia model, a whole brain ischemia reperfusion model, a lipopolysaccharide infection model and a rat brain hemorrhage model, and the 3,5,3',4'-trihydroxy stilbene-3'-O-beta-glucoside for injection is promoted to have a potential therapeutic effect on the brain edema caused by various reasons. Active ingredients of the 3,5,3',4'-trihydroxy stilbene-3'-O-beta-glucoside can be extracted from plants, the drug used is cheap, easy to obtain and good in market prospect.