In this paper, the TiN/TiAlN duplex coatings were deposited on SKH51 tool steel by means of multi-arc ion plating. By means of SEM, Vickers microhardness tester and scratch tester, the effect of target current levels on the surface morphology and mechanical properties of TiN/TiAlN duplex coatings on SKH51 tool steel was studied. During deposition, the effect of target current on microstructure and mechanical properties is responsible for the number, energy of emission target particles and distribution of target droplets. It was found that the thickness and microhardness of coatings, and the number of droplets with diameter more than 2 m increased with target current increasing. The adhesion force between coating and substrate reaches a peak value of 40.5N at 70A. From application view, it is better to control the Ti-Al target current density at 9.88x10-3 A/mm2.