Abstract: Based on the five-strand caster tundish in a domestic steel plant，water modeling system with the 1 : 3 similarity ratio is set up to study the effect of the different internal structure on fluid flow characteristics of tundish according to the similar principle. The results show that the unreasonable internal structure of prototype tundish and different flow characteristics between outlets with large dead zone volume and unfavorable mixing effect. The field characteristics of tundish are improved remarkably by optimizing the internal structure design. Of which, the scheme VI enjoys the optimal mixing effects for its minimum dispersion degree of mean residence time. The plug volume amounts to 23.84 % with dead zone volume of 10 %, which is decreased by 71.70 ％ compared to the prototype tundish．