The present invention relates to a method for preparing a synthetic-organic-ester-type base oil and the use thereof. The method involves weighing reactants and an auxiliary agent for an esterification reaction, wherein the reactants are a mixed raw material of a polyol and a fatty acid at a molar ratio of hydroxyl to carboxyl of 1 : 4-5; the auxiliary agent comprises, in percentages by weight, the following raw materials: 5-15% of a water-entraining agent, 10-20% of a decolorizing agent, 0.1-2% of a catalyst, and 0.1-2% of an antioxidant; the polyol is selected from pentaerythritol; and the fatty acid is made up of one or more of n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, isooctanoic acid and isononanoic acid. The product prepared by means of the method of the present invention, when used as a base oil for a transformer insulating oil, can not only meet the performance requirements for the transformer insulating oil, but also has a good biodegradability, and the preparation process has the characteristics of a high production efficiency, low emissions, etc.