The invention provides a method for preparing oligomeric proanthocyanidins by utilizing a grape seed extract, belonging to the technical field of separation and preparation of the oligomeric proanthocyanidins. According to the invention, oligomeric proanthocyanidins freeze-dried powder and polymeric proanthocyanidins freeze-dried powder are prepared through dissolving, filtering, vacuum concentration, ultrafiltration, column filling, elution, nanofiltration and freeze-drying by using the grape seed extract as a raw material. The method provided by the invention has high raw material utilization rate, high separation accuracy, good separation effect, high product purity and clear product use, realizes complete utilization of raw materials and complete recycling of the solvent, is free of three-wastes discharge, and is a typical high-tech green process. The oligomeric proanthocyanidins prepared by using the method provided by the invention can be extensively applied in the fields of medicines, health-care products, etc.