Abstract: In this paper, the effect of Al substitution on the magnetic properties and thermal stability of MM₂₈Fe_71-xB₁Al_x（x = 0-4） alloys was studied. The results of XRD showed that the alloys are mainly composed of RE₂Fe₁₄B main phase and α-Fe phase. With the increase of the substitution amount of Al, the coercive force of the alloy increased first and then remained unchanged, and the remanence decreased linearly. Through the DSC analysis, it is confirmed that the reason for the deterioration of the thermal stability of the alloy is related to the decrease of Curie temperature of the alloy with the increase of Al substitution. The results showed that the coercive force of the alloys can be optimized by the addition of Al element. Under the best condition, the coercive force of the alloy can reach 913 kA/m, which is valuable for the preparation of high-performance MM-Fe-B magnets.