The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y2O3 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy dispersive spectrometer. The effectiveness of Y2O3 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The experiment results showed that, the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, γ-Fe and α-Fe phases. With the increase of nano-Y2O3 additives, primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 μm, when nano-Y2O3 additive was 2.54 wt.%. The calculated results showed that, the two-dimensional lattice misfit between the face(001) of Y2O3 and face(100) of orthorhombic M7C3 was 4.911%, which indicated that Y2O3 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3. The addition of Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% And 5.08 wt.% Additions of nano-Y2O3 were developed in this work. And the different hypereutectic Fe-Cr-C The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy dispersive spectrometer. The effectiveness of Y2O3 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The experiment results showed that the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, γ-Fe With the increase of nano-Y2O3 additives, the primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 μm, when nano-Y2O3 additive was 2.54 wt.%. The calculated results showed that, the two-dimensional lattice misfit between the face (001) of Y2O3 and face (100) of orthorhombic M7C3 was 4.911%, which indicates that Y2O3 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3.