A series of TiSiN films inserted by CrAlN nanomultilayers with different thicknesses was prepared by reactive magnetron sputtering. The influences of CrAlN layer thickness on the microstructure and hardness of films were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The insertion of CrAlN nanomultilayers destructs the nanocomposite structure of TiSiN film, leading to the decrease of hardness. As the CrAlN layer thickness increases to 2.5nm, CrAlN layers are inclined to grow epitaxially with TiSiN layers in order to lower the interfacial energy. As a result, the TiSiN film can be further strengthened with the maximal hardness of 53.9GPa. As the CrAlN layer thickness further increases to 3.0nm, the epitaxial growth structure between TiSiN and CrAlN layers is broken, resulting in the deterioration of hardness.