In the iron-based high-Tc bulk superconductors,Tc above 50 K was only observed in the electron-doped 1111-type compounds.Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest Tc in these materials.To introduce more electron carriers and less crystal lattice distortions,we study the Th and F codoping effects into the Sm-O layers with heavy electron doping.Dozens of Sm1-xThxFeAsO1-yFy samples are synthesized through the solid state reaction method,and these samples are carefully characterized by the structural,resistive,and magnetic measurements.We find that the codoping of Th and F clearly enhances the superconducting Tc more than the Th or F single-doped samples,with the highest record Tc up to 58.6K when x =0.2 and y =0.225.Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.