Abstract: Nozzle clogging is one of the most famous problems during casting aluminum killed steel. Nozzle clogging can be divided into four kinds according to the position, ladle nozzle clogging, stopper head beard, upper nozzle clogging and SEN clogging, which summarized combining with production practices. The middle-size inclusions plays big role in clogging, which usually results from secondary oxidization. In the meantime, low casting speed would increase the probability of clogging, and inappropriate calcium treatment would make it happens much more seriously. In order to prevent nozzle clogging, the cleanliness of molten steel should be higer, and the measures for preventing secondary oxidization should be taken during casting, and w（Ca）/ w（Alin）≥1.2 should be ensured during calcium treatment. The rate of clogging decreased from 20.6 % to 4.52 %, and the heat number of sequence increased from 8.2 to 10.3 after taking the above actions.

Key words: nozzle clogging, aluminum killed steel, calcium treatment, secondary oxidization