Abstract: Nano-composite alloy Nd_4.5Fe₇₇B_18.5 was prepared by melt quench, annealed under Ar gas protection. The best magnetization properties of the sample were attained by annealing at 660℃ for 10 min. The micromagnetic behavior of the sample is much more complex and full of various interactions because of nanostructure and dual phase composition. The first order reversal curves (FORC) diagram was employed to research the magnetization mechanism and characterize inner interactions. The experimental FORC diagram shows that there are apparent reversible magnetization and irreversible magnetization, coupling each other characterized by the negative peak. The asymmetry and migration of the irreversible peak show strong interactions among magnetic moments, and the whole magnet shows demagnetizing effect, which is proved by the δM curve method.