Nanocrystallite　TiN　films　were　deposited　on　W18Cr4V　high-speed　steel　(HSS)　substrates　using　pulsed　d.c.　bias　multi-arc　ion　plating,　the　mechanism　of　the　super　hardness　of　the　nanocrystallite　TiN　films　was　investigated.　The　results　show　that　the　film　thickness　is　2-3　μm,　the　crystalline　size　is　about　13-16　nm,　and　especially　the　nanocrystallite　TiN　films　hold　super　hardness　of　36-43　GPa.　The　measured　hardness　of　annealed　nanocrystallite　TiN　films　at　elevated　temperature　confirm　that　the　super　hardness　of　the　nanocrystallite　TiN　films　are　produced　not　only　by　the　ion　bombardment　induced　residual　stress　within　the　film,　but　also　due　to　the　decrease　of　crystalline　size,　dense　microstructure　and　the　film　deposition　onto　the　strongly　preferential　orientation　with　the　(111)　plane,　which　is　the　atomic　closed　arrangement　plane　of　f.c.c.　TiN.