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.