In view of the service failure and low continuous casting production efficiency due to the corrosion of refractories at the slag-line in submerged entry nozzles, a submerged entry nozzle for low-carbon aluminum killed steel continuous casting in one steel plant was sampled and taken as the research object to analyze the causes and the mechanism of refractory corrosion at the slag-line. The results show that the core issue of the corrosion and necking of the slag-line materials is that the slag-line material are eroded, dissolved, and reacted by the mold flux gradually. Therefore, it is important to suppress or avoid the contact and reaction between the mold flux and slag-line materials.