The invention discloses a method for preparing hyperin from Dogbane leaves, which comprises the following steps: firstly. determining the optimum extraction temperature, a separation material and the concentration of an eluting agent; secondly, regulating the pH value, and extracting with a solvent having high hyperin dissolving and extracting power, thus obtaining a liquid extract; thirdly, heating at 80-85 DEG C under reflux of ethanol or methanol, and extracting; and finally, standing and crystallizing at a preferable cooling temperature, thus effectively separating the hyperin and isoquercitrin which are two flavonoid glycoside components having similar properties. In the invention, the hyperin is further purified by preparing a liquid phase; and a moving phase is examined and determined by methodology, and is subjected to targeted and efficient separation and purification based on the absorption wavelength of the hyperin, thus obtaining the hyperin having purity up to 90-99%. Thehyperin conforms to the requirements for Class A active pharmaceutical ingredients.