Abstract: High purity crystalline boron powder and pure aluminum powder were used as raw materials, and blended at boron mass fractions of 70%, 74%, 78%, 82%, seperately. The in situ synthesized AlB₁₂/Al composites were prepared by powder metallurgy process at a sintering temperature of 1 500 ℃. An equivalent neutron shielding property calculation model was established. The microstructure, mechanical property and neutron shielding property of the composites were investigated. The results show that the main phase of the composites was AlB₁₂, and the bending strength was not less than 40 MPa. With the increase of boron content, the bending strength was basically unchanged. The composites （with a thickness of 100 mm） could shield about 81% fast neutrons generated by ²⁵²Cf and 76% fast neutrons generated by ²⁴¹Am-Be neutron sources at a boron mass fraction of 70%. The model calculation showed that with the increase of boron content, the fast neutron fluence attenuation ratio of the composites changed little, and the fast neutron shielding property was not significantly improved; its thermal neutron shielding efficiency （reaching up to 98.89% at a thickness of 20 mm） was higher than that of traditional neutron shielding materials including polyethylene and concrete, and was close to that of aluminum-based boron carbide （with boron mass fraction of 31%） with the same thickness. The prepared composites had high boron content, moderate mechanical property and good neutron shielding property.