Abstract: The Al-Nb-B interalloy was prepared by the in-situ reaction method.The microstructure of Al-Nb-B inter-alloy was investigated and the influence of Al-Nb-B interalloy alloy on the microstructure and room temperature tensile properties of Al-12Si-4Cu-2Ni-1Mg alloy were studied.The results show that the NbB₂ and Al₃Nb particles can be observed in Al-Nb-B interalloy alloy. The Al-Nb-B interalloy can refine α-Al grains and reduce the secondary dendrite arm spacing in Al-12Si-4Cu-2Ni-1Mg alloy, furthermore, the tensile property of the alloy is improved at room temperature. When the addition amount of Al-Nb-B interalloy is 2.5wt%, the average grain size of α-Al is 128.4 μm, and the secondary dendrite arm spacing is 11.67 μm, which is decreased by 21.5% and 32.3% respectively compared with that of the matrix alloy. With the increase of the amount of Al-Nb-B interalloy, the tensile strength of Al-12Si-4Cu-2Ni-1Mg alloy shows a gradual increasing trend. When the amount of Al-Nb-B interalloy is 2.5wt%, the tensile strength of Al-12Si-4Cu-2Ni-1Mg alloy is 237MPa, which is increased by 10.7%compared with that of the matrix alloy.The fracture morphology analysis shows that the fracture of Al-12Si-4Cu-2Ni-1Mg alloy is brittle fracture and the fracture mechanism is cleavage fracture.