Abstract: The direct catalytic decomposition of NO in flue gases by Cu - ZSM - 5 has potential application. However，there are different kinds of alkali metals in high⁃temperature flue gas，and the mechanism of the effect of alkali metals on the catalytic decomposition of NO by the Cu-ZSM-5 is still unclear. In this paper，the alkali metals Na and K were loaded onto the Cu-ZSM-5 catalyst prepared by the ion exchange method using liquid phase impreg⁃ nation. The effect of alkali metal loading on the direct catalytic decomposition of NO conversion of the fresh Cu- ZSM-5 catalyst was investigated and its catalyst skeleton structure，pore pattern，copper species，chemisorbed oxygen and oxygen desorption from the active species were analyzed by means of characterization techniques such as the XRD，BET，SEM，TEM，XPS，H2 -TPR and O2 -TPD. The research results show that the conversion of NO for cata⁃ lytic decomposition over the Cu-ZSM-5 catalyst is 53% at an optimum reaction temperature of 550 °C . With the in⁃ crease of alkali metal Na and K loading，the direct catalytic decomposition NO conversion rate of the Cu-ZSM- 5 catalyst is significantly inhibited，and the alkali metal K causes a significantly higher reduction in the NO conver⁃ sion rate of the catalyst than the alkali metal Na. The unique three⁃dimensional cross⁃pore structure within the ZSM- 5 molecular sieve，which can be disrupted by alkali metal K，causes the catalyst skeleton structure to collapse，bloc⁃ king the pore channels and further preventing the contact of the reactant NO with the active site Cu-O-Cu2+， leading to a reduction in the NO conversion. The active component Cu-O-Cu2+ site can combine with the alka⁃ li metals Na and K to deactivate the catalyst， transforming it into the new copper species CuO particles. And as the content of the alkali metals Na and K increases，the amount of CuO also gradually increases，and the CuO par⁃ ticles can occupy the catalyst pore channels and cover the outer surface of the catalyst，resulting in a reduction in the specific surface area and pore volume of the catalyst micropores. The alkali metals Na and K inhibit the redox cycle between the catalyst active components Cu-O-Cu 2+ and Cu-□-Cu 2+ ，which in turn prevents the catalytic de⁃ composition of NO to N2 and O2 .