Abstract: In order to solve the problem of nozzle blockage caused by Al-C refractory for smelting yttrium based rare earth treated steel in a steel plant, the composition of the nodule of the nozzle was analyzed with SEM and XRD, and the junction of the nodulation layer and the nodule and the nodule was scanned.The results show that the main source of the nodule is the precipitation of high melting point compounds such as rare earth aluminates and silicates in molten steel, and the erosion of the rare earth steel liquid to the lining of the steel.The nodulation mechanism of the Al-C material in the application of yttrium based rare earth treatment steel is objectively analyzed by the phase diagram.