Abstract: Oil leakage, whose cause is difficult to find, is one of the most common defects occurring in oil-filled terminals. Aimed respectively at Japanese-style and European-style oil-filled terminals, this work listed out the possible causes of oil leakage and the ways to find this kind of defect, by analyzing structure of the two kinds of terminals. A case of oil leakage defect occurred in a 220 kV terminal was provided, to show the analysis and treatment process of the defect. In addition, the operation and maintenance strategy of oil-filled terminals and prevention measures of oil leakage were put forward. This work provides scientific ideas and valuable experience for the cause analysis and elimination treatment of similar defects.