Objective To study the effects of pulsed bias duty cycle on the microstructure and hardness of TiN / TiAlN multilayer coatings. Methods Five TiN / TiAlN multilayer coatings with different pulsed bias duty cycle were deposited by the pulse biased arc ion plating method on M2 high speed steel substrates, and the microstructure, composition, phase structure and hardness of the multilayer coatings were investigated. Results TiN / TiAlN multilayer coatings surface exhibited a typical growth morphology prepared by arc ion plating. The amount of macroparticles was significantly reduced with increasing pulsed bias duty cycle. The increase of pulsed bias duty cycle also caused the decrease of Al / Ti atomic ratio in the multilayer coatings. Conlusion TiN / TiAlN multilayer coatings preferred (111) orientation growth, and meanwhile contained (311) , (222) and (200) crystallographic structure. The nanohardness of five multilayer coatings was higher than 33 GPa. At 20% pulsed bias duty cycle, the super hard coatings were prepared.