Abstract: Taking the mold of No.1 continuous slab-casting machine in Baosteel as the object, a multi-phase model was applied to simulate the velocity, temperature fields and gas distribution of molten steel with argon injection. The results indicate that the velocity of upward flow increases, the lower re-circulation region appears small, and the temperature gradient decreases. Argon bubbles distribute unevenly and the gas holdup of liquid steel in the upper region is far higher than that of the lower region.