The size of austenite grain plays an important role on the hot ductility of continuous casting slab， and the abnormal large austenite grain also relate to the defects on the strand surface. The results of experimental research on the effect of holding time at 1 350 ℃ on austenite grain size of J55 are compared with related literatures. It shows that the austenite grain size of J55 gets coarser with the increase of holding time at 1 350 ℃.With reference to previous researches， to get a similar level of austenite grain size in the process of continuous casting， the sample of J55 should be held for at least 30 minutes at 1 350 ℃.The results also suggest that the way usually used for high temperature thermal tensile test simulation to test the hot ductility of specimens is probably not considering the size of austenite grains during continuous casting， the results of which may not represent the hot ductility of high temperature slab.