The invention discloses a catalyst coating and a preparation method thereof. By adding a modified catalyst ZnO into the coating, the mechanism that organic harmful substances are degraded in the presence of the catalyst ZnO is well utilized. By the catalyst coating, the problem of the addition of the harmful substances during the production of the coating is completely solved and the potential safety hazard of the coating is removed; experimental results show that the catalyst ZnO powder and modified ZnO dispersion liquid have excellent formaldehyde purifying, degrading and removing functions, antibacterial and mildew-proof functions and the like, by adding the catalyst ZnO powder and modified ZnO dispersion liquid into the production of the coating and in a form of wall decoration, the catalyst coating is a truly functional novel coating capable of efficiently removing harmful substances such as free formaldehyde and toluene and can take effect for a long term.