Pure Ir coating was produced by double glow plasma technology. Growth mecha­nism of the Ir coating was investigated. The Ir coating was composed of irregular compacted columnar grains with lots of nanovoids appeared on the interface between the coating and the substrate. The Ir coating was polycrystalline with a preferred (220) orientation due to the initial nuclei with preferred growth on the surface of the substrate. The formation mechanism of the Ir coating depended on kinetic adsorp­tion and di?usion process with nucleation, coalescence and thickness growth. At the beginning of the deposition process, the growth mode of the coating was mainly con­trolled by the nucleation rate. Due to the low substrate temperature resulting in low mobility of the deposited atoms, some micropores and nanoviods were present at the interface. With the deposition process, the substrate temperature was increased and then kept steady. The growth of the coating was governed by the growth rate. The high substrate temperature supported enough energy to surface mobility of adatoms.