The nanocrystalline alumina abrasive, with its excellent versatility and high-precision grinding capability, has become a cost-effective choice for various applications in fields such as mechanical manufacturing, bearings, molds and automobiles. In this study, nano microcrystalline alumina was synthesized by sol-gel process, with boehmite (γ-AlOOH) as raw material, MgO and La2O3 as additives. The effects of MgO and La2O3 additives on the phase transformation, phase composition, microstructure and mechanical properties of nanocrystalline alumina were investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy and ab initio molecular dynamics simulation. The results show that MgO and La2O3 composite additives can reduce the transformation temperature of alumina from the intermediate phase θ-Al2O3 to α-Al2O3 from 1 257 ℃ to 1 105 ℃, lower the densification temperature of the material from 1 600 ℃ to 1 350 ℃, and reduce the grain size of nanocrystalline alumina from 1.04 mm to 120 nm, thus realizing the low-temperature dense sintering.