Abstract: The austenite grain growth behavior of two high-strength marine steels containing Nb under different austenitizing conditions was studied.The effect of the original austenite grain size on the martensitic transformation was studied by using EBSD technology.The results show that the austenitizing temperature and holding time are positively correlated with the austenite grain size, but the austenitizing temperature has more significant effects on the grain size.In the low-carbon composition system, Nb has more obvious inhibitory effects on the growth of austenite grains.The size of the original austenite grains has an effect on the structure after quenching.After the transformation of the original austenite structure with smaller grains, the large-angle grain boundary ratio is larger, and the distribution is uniform, and the toughness is better.Based on the data obtained from the experiment, a kinetic model of austenite grain growth of the test steel is established.