In order to study the effect of modulation ratio on the structure and properties of Cr/CrN/Cr/CrAlN multilayers. Cr/CrN/Cr/CrAlN multilayers with different modulation ratios were prepared on TC4 titanium alloy by arc ion plating. Scanning electron microscope (SEM) was used to observe the surface and section morphologies of the film, and Image-Pro software was used to quantitatively analyze the large particles on the surface. The crystal structure of the film was characterized by X-ray diffraction. The microhardness of the film was measured by Vickers hardness tester, and the binding force (critical load) between the film and matrix was measured by scratch tester. The residual stress of the film was measured and calculated by the substrate bending method. According to ASTM G76-05 standard, AS600-sandblasting tester was used to test the anti-erosion performance. The depth of offset pits was measured by 3D surface profilometer. The results showed that LCr/CrN:LCr/CrAlN modulation ratio was closely correlated with the surface quality of the films. With the increase of Cr/CrN ratio, the surface quality of the films became better and the preferred orientation changed from (111) plane to (200) plane. The hardness of multilayer films decreased with the increase of Cr/CrN ratio, while the bonding force, residual stress and toughness increased first and then decreased, and reached the best when the ratio of LCr/CrN:LCr/CrAlN was 1:2. The sand erosion resistance of multilayer film was also consistent with the main mechanical properties, and it was the best when LCr/CrN:LCr/CrAlN was 1:2. The erosion resistance of multilayer film was 3 times higher than that of TC4 substrate. The fracture surface of the multilayer film revealed a typically brittle feature. When the modulation ratio LCr/CrN:LCr/CrAlN=1:2, the film has the best anti-erosion performance.