In this study, permanent magnetic nanocrystalline Sm₅Co₁₉Hf_0.4 alloy and Sm₅Co₁₉Hf_{0. 4}CNTs_{0. 4} alloy with high room-temperature coercivity were produced. The microstructure, crystal structure and magnetic were studied. The results show that the Hf elements and CNTs mixed added did not lead to phase decomposition of Ce₅Co₁₉ type structure, meanwhile the microstructure possess fine grain size and uniform distribution. Energy Dispersive X-ray Spectrometry (EDX) analysis confirmed that CNTs move into grain boundaries of the nanocrystalline Sm₅Co₁₉Hf_0.4CNTs_0.4alloy, which can improve the coercivity of the nanocrystalline Sm₅Co₁₉ alloy for the grain boundary pinning effect. Rietyeld refinement showed that Hf comes into the Sm vacancy decreasing the lattice parameters and increasing the axial ratio c/a , which furtherly enhance the magnetocrystalline anisotropy , thus strengthen the coercivity of nanocrystalline alloy. In this paper, the results of the study can promote the design of Sm-Co alloy with high magnetocrystalline anisotropy and intrinsic coercivity.