A method and corresponding reactor for depositing metal-nitride thin film with adjustable metal contents. The method includes several first and second half reaction process. By adjusting the ratio of first and second half reaction cycles, metal nitride thin films with different metal contents can be grown. The first half reaction process is the decomposition of metal-organic precursor adsorbed on the substrate surface, leaving behind metal atom layer by light irradiation. The second half reaction process forms metal nitride thin films by the reaction of NH3 plasma and the metal atomic layer on the substrate surface. This method can control the ratio between metal and nitrogen atom content in the film, thus achieving the regulation of film resistivity. In addition, this method offers favorable film step coverage and accurate film thickness control capability, which is significantly applicable for the film meeting the requirement of advanced CMOS integrated circuit technology.