Abstract: Through physical and chemical inspection,the causation of low elastane of wave hoop was analyzed.The result show that during the producting of raw material,there generated a depth of 20 μm ‘metamorphic zone’ on the surface of the steel belt. Formation of this layer of ‘metamorphic zone’ was because external reactive nitrogen atoms reacted with aluminum of the steel and produced stable AlN compound. This layer of ‘metamorphic zone’ could not be strengthened by the final heat treatment after formation of the wave hoop, so elastane of it was lowered.