The preparation of nanometer aluminum nitrogen (AlN) films with uniform lattice arrangement is of great significance for the manufacture of high-frequency surface acoustic wave (SAW) device. We put forward the two-step growth method and the annealing treatment method for the deposition of (100) AlN thin films. The results show that when the sputtering pressure is 1.2 Pa and the ratio between N₂and Ar is 12:8, the influence of lattice thermal mismatch and anti-phase is the smallest during the nucleation growth at low-temperature stage of (100) AlN/(100) Si films. The root-mean-square (RMS) surface roughness of AlN prepared by the two-step method is reduced from 6.4 nm to 2.1 nm compared with that by common deposition process.