Natural ester transformer oil is easy to oxidize due to its high content of unsaturated fatty acid, while the transformer will dissolve a small amount of oxygen in the oil due to the effect of oil tank and air or leakage of sealing equipment. Based on this, the thermal aging characteristics of natural ester transformer oil under micro-oxygen were studied, the electrical properties, oil chromatogram characteristics and Pearson correlation coefficient of the oil samples under different aging time are analyzed. The results show that the electrical properties of natural ester transformer oil can be delayed to some extent by the action of timely micro-oxygen; the characteristic gases of thermal aging of oil-paper insulation of natural ester transformer are CO2 and C2H6; there is a strong correlation between the electrical properties of natural ester transformer oil and CO2-C2H6 (the percentage difference between dissolved CO2 and C2H6 in oil samples) in the oil chromatogram.