The invention provides an oil immersion type power transformer. The oil immersion type power transformer comprises a transformer shell and a pipe set which is arranged on the inner wall of the transformer shell and is used for circulated flowing of cooling liquid, wherein the pipe set comprises an inlet and an outlet. In operation, heat energy produced by windings and an iron core and the like in the transformer is transferred to the pipe set by an effect of heat conduction and heat convection of transformer oil; the pipe set transfers the heat to the cooling liquid therein in a heat transfer manner; and the cooling liquid absorbs the heat and circularly flows to take away the heat to realize temperature reduction of the transformer, so that the temperature of the transformer is increased to satisfy the national standards. External corrugated heat-radiating fins are replaced with the pipe set arranged on the inner wall of the transformer, the volume of the oil immersion type transformer is effectively reduced, the oil immersion type transformer is convenient to transport, and the transportation cost is decreased.