Diamond like carbon coatings with different thickness have been prepared on Ti alloy substrate by rf plasma enhanced chemical vapor deposition (rf PECVD), their surface morphology and mechanical properties were analyzed and evaluated by AFM, nanoindentation, scratch test, friction test and fretting wear test. The results show that: with the increasing of coating thickness, the surface roughness sharply increases, then significant decreases, at last tending to stable; the hardness and bond strength increase with thickness, but the friction coefficient decreases; and the friction coefficient of DLC coatings against corundum obtained by fretting test decreases with the increase of relative humidity to be below 0 1 in an aqueous condition. All of that are beneficial to their biomedical applications in body fluids.