The influences of coiling temperature and cooling condition on structural transformation of the hot-rolled tertiary oxide scale formed under continuous cooling conditions were studied by thermal gravimetric analyzer.The fourth oxide scale formed under different conditions were classified and plotted.Because the oxide scale structure transformation is diffusion-controlled and the transformation law is similar to “C” curve,the eutectoid transformation nose temperature is 450 °C.Under condition of low temperature and high cooling rate,ion diffusion behavior is restricted so that the eutectoid reaction is suppressed,resulting in that the fourth oxide scale is mainly made up of pre-eutectoid Fe3O4 and Fe O without eutectoid products.From scale structure transition diagram,the eutectoid reaction process was affected by coiling temperature and cooling rate,leading to various scale structures. The influences of coiling temperature and cooling condition on structural transformation of the hot-rolled tertiary oxide scale formed under continuous cooling conditions were studied by thermal gravimetric analyzer. Fourth oxide scale formed under different conditions were classified and plotted. is diffusion-controlled and the transformation law is similar to “C” curve, the eutectoid transformation nose temperature is 450 ° C.Under condition of low temperature and high cooling rate, ion diffusion behavior is restricted so that the eutectoid reaction is suppressed , resulting in that the fourth oxide scale is mainly made up of pre-eutectoid Fe3O4 and Fe O without eutectoid products. Scale scale structure transition diagram, the eutectoid reaction process was affected by coiling temperature and cooling rate, leading to various scale structures.