In order to improve the filtering effect of vacuum oil purifier, the author proposes the research and application of high-efficiency compound vacuum oil-gas separation technology based on electric ultra-high voltage transformer integrated oil purifier. The author studies under the condition of constant oil temperature and flow rate, the effect of vacuum degree on the filtering effect of transformer oil vacuum oil filter. Using the research results, a frequency conversion automatic vacuum oil filter is designed, which makes the processing process have the characteristics of simple operation, high degree of automation, and high work efficiency. The test results show that if the transformer oil processed by the variable frequency automatic vacuum oil purifier is new oil, its water content is less than 45 mg/kg and the gas content is less than 12%; when the breakdown voltage is greater than 25 kV, the transformer oil index can meet the following requirements after the equipment is filtered for one cycle: breakdown voltage ≥75 kV; water content ≤5 mg/kg; and gas content ≤0.1% (volume ratio). After one cycle (after 100 min), the variable frequency automatic (three-stage) vacuum oil filter can greatly shorten the time of transformer oil circulating and filtering. Conclusion. The designed frequency conversion automatic vacuum oil purifier is obviously better than other transformer oil vacuum oil purifiers.