The structure optimization of the threestrand tundish in a steel plant was investigated by physical simulation. The experimental results showed that the shortcircuit flow was easy to occur in the prototype tundish because of the small orifice in front of the baffles. Besides, the inclination angle of the diversion hole was small and its direction was opposite to the edge nozzle, which caused the molten steel to flow directly from the edge nozzle. The residence time was shorter, and the proportion of dead zone was up to 41.08%. After optimizing the diversion orifice of the prototype tundish, the residence time of the optimal scheme "U9T1" was extended from 346.50 to 451.83 s, and the dead zone ratio was reduced to 22.29%, with a reduction of 45.74%. This was conducive to the improvement of volume utilization ratio in tundish and had important guiding significance for the actual smelting production.