A one-pot hydrothermal process was adopted to synthesize nano-Fe3O4@MnO2 core-shell catalysts with diverse thicknesses of MnO2 for the high-temperature Fischer-Tropsch (HTFT) synthesis of light olefins. Herein, the effects of the Mn amount on the morphology and catalytic performance of the catalysts were evaluated by Ar adsorption-desorption, X-ray diffraction (XRD), H-2 temperature-programmed reduction (H-2-TPR), H(2 )temperatureprogrammed desorption (H-2-TPD), CO temperature-programmed desorption (CO-TPD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) equipped with energy-dispersive spectroscopy (EDS)-lining, aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with EDS-mapping, and Mossbauer spectroscopy. Both EDS-lining and EDS-mapping had verified the core-shell structure in the fresh samples. The core-shell structure benefited the reduction of Fe3O4, electron donation, and the CO dissociative adsorption while suppressing the hydrogenation reaction. The porous MnO2 shell inhibited the further growth and aggregation of the Fe species. Fe3O4@MnO2 showed the highest light olefin selectivity of 37.4% at a CO conversion of 91.8%. These results constitute a facile method for preparing Fe-based nanocatalysts applied in the HTFT synthesis.