The change and its mechanism of the infrared emissivity of superalloy K424 with deposited Au film before and after heat treatment were investigated. XRD analyses show that the metal elements of the substrate diffused from the alloy into the Au film, and mainly formed the solid solution of Cr in Au, i.e. Au0.7Cr0.3. EDXS analyses show that oxides of substrate metal element were formed on the rough surface of the sample with deposited Au film after heat treatment; while the polished surface of the sample was still Au film. Both the surface state and heat treatment have great influence on the infrared emissivity tested by spectral radiometer, SR5000.