Monolithic AlN，NbN films and AlN/NbN multilayers with different modulation periods were prepared by reactive magnetic sputtering. The films were characterized by X-ray diffraction, X-ray reflectivity and high-resolution transmission electron microscopy. The results showed that the crystal structure of monolithic AlN and NbN films is close-packed hexagonal (hcp) and face-centered cubic (fcc), respectively. The crystal structure of AlN and NbN is hcp and fcc, respectively, in AlN/NbN multilayers. The interfaces between AlN layers and NbN layers are coherent， i.e., c-NbN (111)∥h-AlN(0002). The lattice mismatch of AlN/NbN multilayers is 013%. The thermodynamic calculation revealed that no matter how thickness of AlN or NbN layer is, the AlN layer does not form nonequilibrium structure of fcc, but the equilibrium structure of hcp. The AlN layers grow in the way of hetero-epitaxial coherent growth with NbN layers.