The utility model discloses a small-sized transformer with a high-efficiency cooling function. The small-sized transformer comprises a base plate, side plates, a cooling strip, a magnetic core, a secondary winding, cooling fins, a cooling cover plate, an inner layer coil, an outer layer coil and a primary winding, wherein the base plate is positioned at the bottom of the transformer; the primary winding and the secondary winding are arranged above the base plate; the middle parts of the primary winding and the secondary winding are provided with the magnetic core; the cooling strip is arranged in the magnetic core; the surface of the magnetic core is provided with the inner layer coil; the outer surface of the inner layer coil is provided with the cooling fins; the outer layer coil is arranged on the outer surfaces of the cooling fins; the cooling fins, the outer layer coil and the inner layer coil form the primary winding and the secondary winding; the side plates are arranged on at the two ends of the base plate; the upper ends of the side plates are provided with the cooling cover plate; the cooling effect of the coil is greatly improved by changing the arrangement of the coil on the winding, then the cooling effect of the magnetic core is increased by changing the magnetic core structure, and finally the cooling effect of the transformer is improved by increasing the winding coil and the heat transfer speed of the surface of the magnetic core.