The invention provides an electromagnetic wave absorbing coating and a preparation method thereof. The coating comprises amino resin, a levelling agent, distilled water, waterborne epoxy acrylate resin, a dispersing agent, a defoaming agent, aluminum powder, ultrafine talcum powder, precipitated barium sulfate, zinc phosphate and an antirust agent; moreover, due to addition of a spirulina chiralmicrowave absorbing agent, the coating is endowed with an electromagnetic wave absorbing effect. By reasonably designing the components and contents of the components, the coating film can reach 100mu m or above, the waterproofness is higher than 240h, salt mist resistance is higher than 200h, and the electromagnetic parameter test proves that the dielectric constant is changed slightly, magnetic conductivity is changed fiercely, and magnetic loss is increased obviously. The electromagnetic wave absorbing coating has strong adhesion to an iron base material, is friendly to the environment, has excellent anti-rust andanti-electromagnetic-wave characteristics, can be brushed on the surfaces of steel pylons to absorb electromagnetic waves, and has a wide application prospect in the fields of power transmission iron electric devices and the like.