Abstract: In view of the high quality requirements of stainless steel for high-grade welded pipes in the medical field, the causes of different degrees of slag in the weld of conventionally produced 316L stainless steel cold-rolled plates after welding and its influence on the actual use were analyzed. The comparative welding tests were carried out on 316L stainless steel cold-rolled plates with different S element contents. The results show that the weld slag was mainly formed by the solidification of Al₂O₃-SiO₂-CaO composite inclusions after floating to the surface of the molten pool. Increasing the depth of the molten pool could inhibit the floating of inclusions to the surface to form slag. Increasing the content of the surface active element S that could change the surface tension temperature gradient could make the surface tension temperature gradient of the molten pool positive, thereby forming a deeper and larger weld molten pool.