Two series of Fe/Cu/K catalysts were prepared by co-precipitation (CP-xK) and by co-precipitation accompanied with hydrothermal treatment (HY-xK), respectively. The catalysts were investigated by N-2 adsorption, X-ray diffraction (XRD), Mossbauer effect spectroscopy (MES), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), H-2 temperature-programmed reduction (H-2-TPR) and thermogravimetric analysis. N-2 adsorption revealed that HY-xK catalysts displayed relatively low surface area, but generated additional macropore. XRD and SEM showed that HY-xK catalysts were well grown crystallite, while the CP-xK catalysts were amorphous. In addition, hydrothermal treatment remarkably influenced the growth orientation of hematite nanocrystals, resulting in the preferential exposure of the (110) plane. HRTEM also indicated that HY-1.32K was dominated by Fe2O3 nanocrystals with (110) plane, and the CP-1.38K primary particle mainly exposed (104) plane. The H-2-TPR profiles for the two series of catalysts were similar, though the merged and smooth peak of HY-xK catalysts possibly suggested that the component elements were more uniform. MES and XRD indicated that the catalyst after hydrothermal treatment can be easily reduced into active carbide phases in Fischer-Tropsch synthesis (FTS) reaction. In FTS reaction, the HY-xK catalysts showed higher activity and better stability than the CP-xK catalysts given comparable K content.