The invention provides a method purifying angelica dahuricae and the method is a process which uses angelica root condensate extract as raw material and adopts the crystallization process to prepare and purify coumarin. The method comprises the following steps: firstly dissolving coumarin condensate in hot petroleum ether or mixed solvent, secondly reducing the temperature slowly, controlling the crystallization process to precipitate the target product; and standing the solution, and filtering to obtain the crystalline product. Through the quantitative analysis of the high performance liquid chromatography method, the sum of the contents of three coumarin compounds, namely imperatorin, phellopterin and isoimperatorin is up to more than 98%. The method of the invention has the advantages of simple process, low cost, high yield, mild conditions, stable product quality and the like and has good industrial application prospect.