<p>A coupled numerical model integrating molten steel flow, solidification behavior, matrix deformation behavior, and surface crack tip extension was developed. Following validation of temperature evolution and strain–stress curve, the model was used to investigate slab crack propagation with various strip feeding ratios during continuous casting, accounting for variations in crack positions and types. The results show that the “double roll” flow is formed under the limitations of the mold narrow surface, meniscus, and submerged entry nozzle, inducing an easier propagation of crack at the slab narrow surface where the S32654 matrix exhibits higher temperature and lower yield strength. The feeding strip prevents the jet from washing on the slab narrow surface, significantly reducing the temperature and increasing the yield strength there. As the strip feeding ratio increases, crack propagation becomes more difficult, while surface crack area gradually decreases. Moreover, longitudinal crack propagation occurs most easily, followed by 45° oblique crack propagation, while transverse crack propagation is the most difficult, due to the increasing angle between the directions of stress release and slab casting. The optimal strip feeding ratio should be around 0.75%, stopping the propagation of transversal cracks and 45° oblique cracks, and avoiding adhesion between the solidified shell and the steel strip simultaneously.</p>