The invention provides a modified alumina particle, and a preparation method and an application thereof. The preparation method comprises the following steps: adding aromatic carboxylic acid and alumina particles to an organic solvent, carrying out a reaction at 90-130 DEG C for 2-12 h, washing the obtained product, and drying the washed product at 20-90 DEG C to obtain the modified alumina particle with the aromatic carboxylic acid on the surface. 50-100 parts by mass of the aromatic carboxylic acid is applied to every 100 parts by mass of the alumina nano-particles. The modified alumina particle is used as a polypropylene nucleating agent; and compared with the unmodified alumina particles, the modified alumina particle can significantly improve the crystallinity and mechanical properties of a polypropylene resin composition.