The invention relates to a transformer oil repairing method. The transformer oil repairing method comprises the steps of filtering, dehydrating and degassing degraded transformer oil, and adding a nano-hydrogenation catalyst and isoparaffin, wherein the nano-hydrogenation catalyst is a nickel-supporting zinc oxide/aluminum oxide catalyst, the carbon chain length of isoparaffin is 8-20 and is preferably 12-18, the adding amount of the nano-hydrogenation catalyst in the processed transformer oil is 0.2wt%-5wt% and is preferably 0.5wt%-2wt%, and the adding amount of isoparaffin in the processed transformer oil is 5wt%-10wt% and is preferably 6wt%-7wt%. The transformer oil processed by virtue of the transformer oil repairing method can basically reach the index of primary transformer oil, and the degradation process of the transformer oil can be inverted, so that the service life of the transformer oil is greatly prolonged.