The causes of cavity defects on W600 hot-rolled intermediate billet produced in the one iron and steel company were analyzed by metallographic analysis from the band thickness and the size of the oxidized round spots, metallographic microstructure, the thickness of desilication band near the crack and the high-temperature mechanical property of the electral steel. The results comfirm that the cavity defects of the intermediate billet of the electral steel result from the microcrack which are rooted in all sorts of stress in the slab, the microcrack is oxidized further by the heating process and enlarged further by the rough rolling process.