The microstructure and phase composition of Sm-Fe alloy during quenching process were investigated by means of SEM, XRD, EDX, and AFM, etc. It is indicated that the Sm-Fe alloy cast consists of Sm2Fe17 phase, Sm-rich phase and a mount of a-Fe phase, and the alloy of single Sm2Fel7-phase was obtained after homogenization annealing. The alloy is composed of the Sm2Fe17 phase with Th2Zn17-type structure and a few a-Fe phase, with unhomogeneous grain sizes of about 100 nm when the quenching velocity is 10 m/s. But at 20 m/s, the alloy still contains Sm2Fe17 and a-Fe phases, but the content of a-Fe is increased when compared with at 10 m/s. At the same time, the stable Sm2Fe17 phase starts to convert into sub-stable SmloFe90 phase. At 30 m/s, the alloy is completely composed of SmloFe90 phase with the ThCuT-type structure and homogeneous grain size of40-50 nm.