Abstract: A mathematical model of flow characterization in multi-strand continuous casting tundishes was attempted to put forward, the standard of plotting residual time distribution (RTD) curves was definitely presented and a relative calculation method was proposed. The feature of dead region was carefully studied and. a method to calculate its volume fraction was given in the model. What' s more, the model considers bypass flow and proposes a method to calculate its volume fraction. Experimental results show that this new model can better capture the difference between the reality flow pattern and the ideal plug flow pattern and reflects the feature of plug flow.