Abstract: SmCo_7-xHf_x (x=0, 0.1, 0.15, 0.2, 0.3) alloy ribbons were prepared by melt-spun at 40 m/s. The phase composition, microstructure and magnetic properties of SmCo_7-xHf_x alloys were investigated. The results show that, the metastable phase of TbCu₇ structure can be obtained with the increasing of Hf substitution, as well as the lattice constants a and c. The c/a ratio is 0.82~0.83, and the grains become finer and uniform. The optimum magnetic properties (B_r=0.55 T and H_c=1 084 kA/m) were obtained with x=0.2 Hf substitution. The Hf substitution could also improve the alloy high temperature performance observably. The coercivity temperature coefficient is improved from -0.21 %/℃ to -0.18 %/℃, with a growing range around 14.3%, at the temperature range of 27~400 ℃.