Scanning electron micrope (SEM) and energy dispersive spectroscopy (EDS) were used to analyse the microstructural morphology and composition of lamination defects on the No.1 surface of 304 austenitic stainless steel. Combined with the study of the flow behavior inside the crystallizer, the defect was identified as being caused by slag coiling during the casting process. In the production of 304 stainless steel, measures such as controlling the selection of the submerged entry nozzle, limiting the insertion depth, and stabilizing the casting speed in the continuous casting process are implemented to stabilize the level of molten steel in the crystallizer, effectively reducing the likelihood of slag coiling. In subsequent processes, the surface quality inspection of the cast slabs is enhanced, and the descaling process is optimized, further lowering the overall downgrading rate caused by lamination defects. Ultimately, the occurrence rate of lamination defects on No. 1 304 stainless steel decreases from 15.0% to below 3.0%.