Abstract: Surface quality problems such as cold shut and blemish usually appear during the EBCHM for ultra-long and ultra-thin(8 000 mm×210 mm) titanium slab ingot, resulting in the low quality production of titanium strip coil. The evolution of solid-liquid interface can affect the interface between the crystallizer and the titanium slab ingot, so as to affect the structure feature and the surface quality. In this work, the morphology of solid-liquid interface was studied based on the mix Lagrangian and Eulerian non-steady algorithm(MiLE), and the mechanism of defect was analyzed.Resultsshow that when the input energy of crystallizer's border increases, the blemish hardly appears because of the thin solidification layer in the surface of ingot. Experiment validates that when the pouring temperature is 2 123 K and appropriate amount of energy is input near the crystallizer, the ultra-long and ultra-thin TA1 slab ingot of high surface quality can be produced.