The invention discloses vegetable insulating oil, which is mainly prepared from the following raw materials in percentage by weight: 90 to 95 percent of vegetable oil and 2 to 5 percent of antioxidant. The invention also provides a method for preparing the vegetable insulating oil. The product is a novel vegetable insulating oil, is insulating oil for a transformer, is a high-performance insulating material extracted from renewable plants, and has the characteristics of environment friendliness, safe operation, long service life, high overload capacity, low carbon, energy saving and the like.