The invention discloses a rectangular radiator with single-side heat conduction planes. The radiator comprises a strip-shaped base and main insertion pieces arranged on the two sides of the base. A trapezoidal groove is formed by the main insertion pieces and the base. An auxiliary insertion piece is arranged on one side of each main insertion piece. The auxiliary pieces are arranged on the outer portion of the trapezoidal groove. Multiple sub insertion pieces are arranged on each auxiliary insertion piece. The two sides of the base are provided with the heat conduction planes. The rectangular radiator is simple and reasonable in structure, due to the fact that the position and the shape of fins are improved and the heat conduction planes are arranged to make contact with a heating object, two heat conduction manners of heat conduction and heat radiation are combined, and the heat conduction efficiency and the heat radiation efficiency of the whole radiator are improved.