Abstract: A new casting speed reduction technology of tundish tail billet has been developed in base of final cast close up operation in order to solve the problem of high waste rate of the factory in ultraheavy plate continuous casting production, which because superficial quality unqualified of tail billet peeling treatment. The numerical simulation of the influence of the new technology on the flow field in the tundish was carried out which applied computational fluid dynamics software FLUENT. The final scheme of tail billet casting speed reduction has been established: residual casting of molten steel is 10 t, and casting speed reduction operation should be started from the speed of 0.9 m/min, the speed reduction of 0.05 m/min each time, the duration time on each speed is:2-5-10-5-10-5-10-5-10-5-10-5-10-10 s. The close up operation should be started in the speed of 0.2 m/min and the duration time is 350 s. The optimization of tundish tail billet casting speed reduction scheme can save the tail billet casting speed reduction time 243 s, reduce casting tail billet length 1.1 m（4.62 t）, decrease tail billet 2.62 t(residual casting of molten steel increased 2 t). After the optimization scheme of tail billet casting speed has been adopted, waste products occurrence rate of ultraheavy continuous casting tail billet in the factory dropped to 18.9 % from 30 %.

Key words: ultra-heavy plate, tundish, CFD, tail billet；casting speed reduction