The invention relates to a preparation method of oligomer grape seed procyanidin. The preparation method comprises the following steps that: firstly, after grape seeds are washed and cleaned by clear water, the grape seeds are added into an ethanol solution, leached, filtered and removed, and an extracting solution is collected; secondly, the extracting solution is regulated by an NaOH solution, slightly stirred to separate out a brick-red procyanidin coarse sediment, and the sediment is filtered and collected; thirdly, the sediment is put into the ethanol solution and dissolved, and filter liquor containing dissolved procyanidin is collected; and finally, the filter liquor is filtered by a nano filter film, oligomer procyanidin intercepted and deposited on the filter film is collected, the sediment is respectively washed by acetone and ethanol, and an oligomer procyanidin product is obtained after the sediment is put into a drying oven and dried.