The invention discloses a selenium-rich rapeseed oil preparation method using selenium-rich garlic essential oil as an antioxidant. The preparation method comprises: selecting selenium-rich garlic squamous bulb, carrying out natural air drying, removing the root portion having soil, paving to achieve the single layer of the garlic squamous bulb, carrying out microwave power treatment on the garlic squamous bulb, taking out, peeling, mashing, carrying out microwave pretreatment and carbon dioxide supercritical extraction to obtain garlic essential oil or extracting garlic essential oil with a selenium content of 20-25 mg/kg from the selenium-rich garlic squamous bulb through a Soxhlet extractor method by using acetone as a solvent so as to be used as the natural anti-oxidation additive of high quality cold-rolled rapeseed oil, adding 0.2-2 parts of the selenium-rich garlic essential oil to 100 parts of high quality cold-rolled rapeseed oil, uniformly mixing, sealing, and storing in a 5-20 DEG C dark environment. According to the present invention, the selenium content of the prepared selenium-rich rapeseed oil is 0.06-0.50 mg/kg, and the prepared selenium-rich rapeseed oil has characteristics of fragrance and long shelf life, and meets the industry standard of the selenium-rich edible oil.