Oil-immersed transformer is based on oil as the main insulation means of transformer, and relies on oil as the cooling medium, such as oil-immersed self-cooling, oil-immersed air cooling, oil-immersed water cooling and forced oil circulation. The main components of the transformer are iron core, winding, fuel tank, oil pillow, breathing apparatus, explosion-proof tube (pressure relief valve), radiator, insulation sleeve, tap changer, gas relay, thermometer, oil purifier and so on.