A CFD-DEM modelling of the densification of uniform tetrahedron particles under air impact was conducted. The effect of air impact on packing structures such as packing density, coordination number (CN), radial distribution function (RDF) were analysed, and the densification mechanisms were discussed based on the analysis of local structure. The void distributions in the packing were analysed using a sphere filling method. The packings after air impact had smaller pores due to the reduction of void with normalized sphere diameter from 0.15 to 0.35. It was observed that the final dense packing had less contacts because of the change of non-stable contacts to more stable face-face contacts. Both dimer and wagon wheel structures increased at the final packing and the increase in the wagon-wheel clusters was more significant than the dimer clusters. The transfer of the dimer structure to the wagon wheel structure during was analogue to the nucleation and growth of crystals. The normal forces distribution exhibited exponential decays for both initial and final packing, and the normal force had a non-linear increase with depth in packings before air impact, while had a linear increase with depth in the packings after air impact.