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2,6-di-tert-butyl-p-cresol (T501) is the most commonly used antioxidant for insulating oils. It has been found that the amount of T501 added to the insulating oil affects the physical and electrical properties of the insulating oil. In this paper, the effects of antioxidants on insulating oils at different concentrations were studied. The research focused on acid value, water-soluble acid or alkali, flash point, kinematic viscosity, volume resistivity and interfacial tension. An aging test was conducted at 115°C to test changes in acid value, sludge, and volume resistivity. Add the same quality insulating paper to the oil sample with the blank oil and T501 added in the amount of 1% (mass fraction), and isolate the oxygen to the effect of furfural before and after the addition of the antioxidant after aging at 130 °C. The results show that with the increase of the amount of antioxidant T501, the interfacial tension, acid value and electrical resistivity will decrease its performance index, but the effect on flash point, viscosity and pour point is not obvious. The aging test by heating the open cup shows that the antioxidant has an obstructive effect on the acid value and the sludge, delays the aging of the insulating oil, but accelerates the aging hydrolysis of the insulating paper. Therefore, it is recommended that the antioxidant content in the insulating oil should not be excessively added. In the insulating oil, the proportion of the antioxidant in the insulating oil should be reduced on the premise that the oxidation resistance can be achieved, and the T501 part consumes the logistics.