Kanthal coatings were fabricated by selective laser melting(SLM) with two kinds of powder, 45-60um and 50-70um in diameter. The coatings surface morphology, microstructure, element distribution, phase structure, and microwave attenuation properties were studied by optical microscope, scanning electron microscopy, X-ray diffraction, and cavity characteristic measurement system. The results indicate that Kanthal coatings have the characteristic of rough surface, porous and flaky structure. The quality factor Q of cavity loaded with coatings fabricated by 45-60um Kanthal sphere powder is lower than that of coatings by 50-70?m Kanthal sphere powder, showing better microwave attenuation properties under the frequency of 2985MHz. Al2O3 thin film and micro void generated in the structure of coatings have the effect of scattering microwave and thus reduce microwave reflection. It is also shown that flattened shape of Kanthal coatings is a good way to suppress eddy currents in high-frequeny electromagnetic field and lead to the formation of easy magnetization planes, which is helpful to enhance the microwave attenuation property. The coating thickness has profound effects on interference loss of microwave. Cavity Q with coating thickness of 0.55mm reached the minimum value of 2280. Kanthal coating is composite material and the main mechanism is attributed to magnetic loss.