The invention discloses a method for increasing breakdown voltage of transformer oil. The method includes the following steps: step 1, measuring breakdown voltage and a particle sum of each phase of transformer oil of a transformer respectively to obtain original data of the breakdown voltage and the particle sum of the transformer oil; step 2, building a gray system model reflecting a relation between the breakdown voltage and the particle sum of the transformer oil; step 3, according to the original data obtained in the step 1 and the gray system model built in the step 2, a quantitative relation between the breakdown voltage and the particle sum of the transformer oil is determined; and step 4, according to the quantitative relation obtained in the step 3, reducing the particle sum of the transformer oil so as to enable the breakdown voltage of the transformer oil to meet a use requirement. By means of the method, the quantitative relation of the particle sum on the breakdown voltage of the transformer oil is determined, the breakdown voltage of the transformer oil is increased by processing the transformer oil, the breakdown voltage of the transformer oil meets a use requirement, and the transformer oil keeps good electric performance.