Completely amorphous ribbons of Sm2Fe17Zr1Nb0.4Cu0.2B0.2 multicomponent alloy, prepared by melt-spinning technique at the wheel speed of ~40 m/s under the argon atmosphere, were achieved. The Sm2Fe17Zr1Nb0.4Cu0.2B0.2 multicomponent alloy is of the negative mixing enthalpy (ΔHmix), for the mixing enthalpy of Fe-B alloy is -26 kJ/mol, significantly lower than Fe-Zr, Fe-Nb and Fe-Sm, promoting the formation of amorphous phase. Detailed microstructural investigations were conducted using scanning electron microscopy and transmission electron microscopy. It revealed that the formation of completely Sm-Fe-Zr-Nb-Cu-B amorphous alloy without obviously precipitation of the second phase. The obtain of completely amorphous structure is conducive to the reconstruction of the microstructure in the later annealing process. The addition of Cu element increases the mixing enthalpy, resulting the reduction of the glass forming ability (GFA) of the nanocrystalline alloys, but it inhibits the formation of α-Fe soft magnetic phase effectively, which is in favor of the improvement of the magnetic properties. The research lays a foundation for the preparation of excellent magnets.