Abstract: Secondary oxidation take places during the air suction process of molten steel as being continuously cast.Focused on in the paper is a description of the test conducted by Pangang Group Chengdu Steel and Vanadium Co.Ltd.,i.e.,sealing the connection section between the ladle bottom nozzle and the shrouded nozzle by different methods to see the change of air suction status of the molten steel in order to analyze the shielded casting effectiveness under different sealing conditions.The test result shows that the argon + gasket method is the most effective sealing measure.