The work aims to study effects of modulation period on structure and mechanical properties of CrAlSiN/TiAlSiN nanocomposite coatings. Periods of coating structure was adjusted by changing revolving speed of substrate (revolving speed as 2, 4, 6 and 8 r/min). Nanocomposite coatings with different modulation periods were prepared by cathodic multi-arc ion plating with CrAlSi and TiAlSi as the cathode arc target materials. Microstructure, chemical composition, surface morphology and cross-sectional morphology of the coatings were measured with X-ray diffractometer, X-ray photoelectron spectrometer, scanning electron microscopy and atomic force microscopy, respectively. Mechanical properties of the coatings with different modulation periods were analyzed with microhardness tester, scratch tester and friction tester. The CrAlSiN/TiAlSiN nanocomposite coatings had the same phase structure at different revolving speed, including CrAl, CrN and TiN phases. Al element was nearly subject to solid solution in CrAl phase. Si element was present in the coating as an amorphous phase or was wrapped with an amorphous compound. With the decrease of the revolving speed, hardness of the composite coatings first increased and then decreased while friction coefficient and RMS roughness first decreased and then increased. The higher the hardness was, the lower the friction coefficient and RMS roughness would be. The hardness and friction coefficient of the CrAlSiN/TiAlSiN nanocomposite coatings are significantly affected by the modulation periods. At the revolving speed of 6 r/min, the coatings have a maximum microhardness of 38 GPa and lowest coefficient of friction (0.375).