Two mixed oxide systems La2-xSrxCuO4±λ(0 0≤x≤1.0) and La2-xTh,CuO4 (0 0≤10.4) with K2NiF4 structure were prepared by varying x values Their crystal structures were studied by means of XRD and IR spectra.The average valence of Cu ion at B site,nonstoichiometric oxygen (λ) and the chemical compo-sition in the bulk and on the surface of the catalysts were measured by means of chemical analysis and XPS The catalytic behavior in reaction CO+NO was investigated under the regular change of average valence of Cu ion at B site and nonstoichiometric oxygen (λ).Meanwhile,the adsorption and activation of the small molecules NO and the mixture of NO+CO over the mixed oxide catalysts were studied by means of MS-TPD The catalytic mechanism of reaction NO+CO over these oxide catalysts were proposed; and it has been found that,at lower temperatures the activation of NO is the rate determining step and the catalytic activity is related to the lower valent metallic ion and its concentration,while at higher temperat Two mixed oxide systems La2-xSrxCuO4 ± λ (0 0≤x≤1.0) and La2-xTh, CuO4 (0 0≤10.4) with K2NiF4 structure were prepared by varying x values ​​Their crystal structures were studied by means of XRD and IR spectra The average valence of Cu ion at B site, nonstoichiometric oxygen (λ) and the chemical compo-sition in the bulk and on the surface of the catalysts were measured by means of chemical analysis and XPS The catalytic behavior in reaction CO + NO was investigated under the regular change of average valence of Cu ion at B site and nonstoichiometric oxygen (λ) .Meanwhile, the adsorption and activation of the small molecules NO and the mixture of NO + CO over the mixed oxide catalysts were studied by means of MS -TPD The catalytic mechanism of reaction NO + CO over these oxide catalysts were proposed; and it has been found that, at lower temperatures the activation of NO is the rate determining step and the catalytic activity is related to the lower valent metallic ion and its concentration, whi le at higher temperat