Mixed insulation oil developed from mineral oil and natural ester can take into account the advantages and disadvantages of mineral oil and natural ester. Mastering the moisture absorption and power frequency breakdown characteristics of mixed oil can lay a foundation for its application in transformer and oil quality control. With mineral oil as a reference

the moisture absorption characteristics of the three-element mixed insulating oil at different temperatures

power frequency breakdown（AC） characteristics under the combined action of temperature and water

and dissolved gas characteristics in oil after multiple power frequency breakdown wer

e studied and analyzed. The results show that the moisture absorption rate and saturated water content of the three-element mixed insulation oil are obviously higher than those of mineral oil

which means the moisture capacity of the three-element mixed insulation oil is superior to that of mineral oil.With the increase of water content in oil

the power frequency breakdown voltage of the three-element mixed insulation oil and mineral oil decreases obviously

but the power frequency breakdown voltage of the three-element mixed insulation oil is stronger to withstand water degradation. When the water content of the three-element mixed insulation oil is less than 70×10

-6

its power frequency breakdown voltage can be maintained above 40 kV in the range of 15 ℃～90 ℃. The results of two-parameter Weibull distribution analysis also show that the power frequency breakdown performance of the three-element mixed insulation oil is better than that of mineral oil. After multiple power frequency breakdown

H

2

and C

2

H

2

are the main types of oil products under power frequency breakdown condition. The percentage of H

2

and C

2

H

2

in dissolved gas produced in three-element mixed insulation oil is higher than that of mineral oil.