The invention discloses a preparation method of a catalyst metal heating surface for reducing NOx in flue gas, and belongs to the technical field of control of flue gas pollutants. The catalyst metal heating surface comprises a metal pipe and a nanoparticle catalytic activity coating cured on the surface of the metal pipe; the catalyst is an iron-based nickel manganese composite oxide, wherein nickel, manganese and iron are subjected to a catalytic reaction in a form of oxides. The preparation method comprises the following steps: curing iron-based nickel manganese composite oxide powder on the outer surface of the metal pipe by adopting a high-temperature spraying method to form a nanoparticle catalytic activity substance coating; performing heat treatment in an oxygen-containing atmosphere. The NO concentration in the flue gas can be reduced to 2%-36% of the original concentration, and emission of NOx into the environment is reduced. Meanwhile, the catalytic activity coating has excellent wear resistance, has extremely slight influence on the heat transfer characteristic, the mechanical strength and other performance of the heating face, and can be widely applied to superheaters and reheaters in combustion equipment and flue gas purification treatment equipment.