Objective To study the effect of modulation period on the properties of nano-multilayers. Methods CrAlN/ ZrN nano-multilayers were deposited with different modulation periods in a magnetron sputtering system, fixing the layer thickness ratio CrAlN : ZrN as 2. 6. To characterize the morphology and structure of the films, the field emission scanning electron microscopy (FESEM) was used. The Dektak 150 surface profiler was used to measure the coatings‘ roughness. Agilent Technologies G200 nanoindentation was used to test the coatings‘ hardness and elastic modulus. Automatic scratch tester was used to measure film critical loads. The toughness of the films was characterized by CPR (crack propagation resistances). Results CrAlN / ZrN nano-multi-layers‘ sections were transgranular columnar structure. When the modulation period was 20 nm, the distinction between layer and layer was clear. The surface of nano-multilayers was dense like the cauliflower. The thickness of nano-multilayers was about 2 microns. When the modulation period was 8 nm, the hardness was 20. 4 GPa. After further increasing the modulation period, the hardness decreased. The critical load Lc2 was 18 N, CPR number was 73. 2, when the modulation period was 8 nm. The nano-mul-tilayer‘s critical load Lc2 and CPR number were higher than other nano-multilayers. At the critical load Lc2 , the coatings were peeled off as the result of crack propagation. And the bright white hot rolled steel substrate was exposed and the nano-multilayers lost the protective effect to substrates. Conclusion Changing the modulation period will affect the nano-multilayer coating‘s toughness under the condition, keeping the multilayer coat‘s thickness and modulation ratio invariable. With the increase of modulation period, toughness properties is improved then descended. The film has the highest hardness and toughness and gets the best comprehensive performance when the modulation period is 8 nm.