By　X-ray　stress　analysis　technique,　a　new　approach　has　been　applied　to　determining　the　yield　strength　of　polycrystalline　TiN　film　with　biaxial　residual　stress　adherent　to　metal　substrate.　By　plasma-assisted　chemical　vapor　deposition　(PACVD),　TiN　film　was　deposited　on　a　strip　of　spring　steel　60Mn　allowing　the　film　to　be　subjected　to　tensile　stress　under　loading　of　the　film/substrate.　The　film　thickness　is　2.5mum　and　the　steel　substrate　thickness　is　1.1mm.　Longitudinal　and　transverse　stresses,　sigma(1),　and　sigma(2)　of　the　film　were　measured　in　situ　by　X-ray　diffraction.　On　the　basis　of　the　experimental　results,　the　effective　stress　(sigma)　over　bar　and　the　effective　uniaxial　strain　(epsilon)　over　bar　(t),　were　obtained.　According　to　the　(sigma)　over　bar　-　(epsilon)　over　bar　(t),　relation,　the　calculated　proof　stresses,　sigma(0.1),　and　sigma(0.2),　of　TiN　film　are　4.2GPa　and　4.4GPa,　respectively.