Abstract: Fe-4Cr-2B-0.5C- (0.1-3)Nb alloy with different Nb content was prepared by induction melting method.By using metallographic microscope, scanning electron microscope, X-ray diffractometer, universal testing machine, rockwell hardness tester and micro vickers hardness tester, the phase, microstructure and mechanical properties of Fe-Cr-B-C alloy with different Nb content were analyzed.By using Origin function simulation, EXPGUI structure refinement, Image-ProPlus image analysis and Image J binary threshold processing software, some results were obtained.The results show that the primary matrix phase of Nb bearing high boron cast iron is mainly martensitic structure, and boron carbide forms network eutectic structure. The alloy is composed of α-Fe, Fe₂B, NbC and other phases. With the increase of Nb content, the hardness decreases from 65.8 HRC to 52.2 HRC, the bending strength increases from 1304.97 MPa to 1731.45 MPa, and the fracture toughness increases from 29.76 MPa·m^1/2 to 32.89 MPa·m^1/2. NbC type boron carbon compounds distribute in the eutectic structure, resulting in the network eutectic broken, and reducing the carbon content of the matrix.Therefore, there is a certain relationship between the change of macrohardness, strength and toughness and the content of Nb element.