Solid-liquid interface morphology of the titanium ingot has great influence on the microstructure during the solidification process. This paper focused on the effect of Crystallizer"s 3D dimension of the ultra-long and ultra-thin TC4 slab ingot on the solid-liquid interface morphology. The results show that when the cross-section length of TC4 slab ingot exceeds 450mm, the cooling capacity of the crystallizer does not increase. When the length exceeds the effective distance, the depth of molten pool and the width of mushy zone will not change with the increase of the length in the crystallizer. Moreover, increasing the ratio of the crystallizer’s length to width is helpful to improve the production quality. The simulation results show that it is better to choose between 4:1 and 6:1. When the height of the crystallizer is higher than 300mm, the depth of the molten pool and the width of mushy zone will not change. Therefore, the certain range theoretical basis was obtained to design the crystallizer’s three-dimension during EBCHM for the ultra-long and ultra-thin TC4 slab ingot.