Abstract: In order to improve the poor amorphous formation ability of Nanomet nanocrystalline soft magnetic materials and the coarse grain size after annealing, Fe_81.3Si₃ B_11.7-xP₃ Cu₁C_x（x=0, 0.5, 1.0, 1.5, 2.0） alloy strip was prepared by single-roll strip spinning method, and the effects of annealing temperature on the crystallization behavior, magnetic domain structure and soft magnetic properties of the alloy strip were systematically studied. The results show that when the annealing temperature T_a＜475 ℃, the internal stress of the alloy is relieved and the performance is slightly improved. As the temperature increases, at 475 ℃≤T_a≤525 ℃, the nanocrystals begin to precipitate and grow, and the performance is optimized. At T_a＞525 ℃, the performance deteriorates due to the overgrowth of nanocrystals and the precipitation of hard magnetic phases. The addition of an appropriate amount of C element can effectively increase the reduced glass transition temperature(T_rg) and improve the amorphous formation ability（AFA） of the alloy. At the same time, the addition of C can refine the grain size of α-Fe（Si）,thereby reducing the coercivity of the alloy. When the C content is x=1, the grain size is 22.4 nm after annealing at 525 ℃, and it has excellent soft magnetic properties of B_s=1.78 T and H_c=7.3 A/m.