The invention relates to a method for extracting brassica rapa l. seed oil by using supercritical carbon dioxide, specially used for deep processing of brassica rapa l. seeds. Taking brassica rapa l. (Brassica rapa L.) seeds as the raw material, the method comprises the following process steps: the brassica rapa l. (Brassica rapa L.) seeds are treated by impurity removal, crushing and filtering, and is extracted by the supercritical carbon dioxide under the conditions that the extraction temperature is 46.10 DEG C, the extraction time is 80.40min and the extraction pressure is 31.65MPa, the brassica rapa l. seed oil extraction yield is 31.893-32.554 percent, and the purity of the brassica rapa l. seed oil is above 99 percent. A process for extracting the brassica rapa l. seed oil by using the supercritical carbon dioxide provides a new method for deep processing of the brassica rapa l. seeds, can efficiently carry out research on extracting the brassica rapa l. seed oil by the supercritical carbon dioxide, has the advantages of strong operability, favorable safety, higher yield, favorable repeatability, high extration yield, simple process, high product purity, non pollution and the like and can be used for extracting the brassica rapa l. seed oil in production.