The meniscus shell plays an important role in slab quality and process operation for continuously cast steel.One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscillation and liquid steel flow to generate disturbance of casting.The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects.The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending.The formed crack may also expand and propagate due to the following secondary cooling and straightening behavior.The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of solidifying shell.The inter-dendrite bridging is also likely to be formed to produce other internal defects,such as air hole and solute enrichment in the residual molten steel located in the bridging area. The meniscus shell plays an important role in slab quality and process operations for continuous cast steel. One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscillation and liquid steel flow to generate disturbance of casting. The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects. results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending the formed crack may also expand and propagate due to the following secondary cooling and straightening behavior. the primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of the solidifying shell. The inter-dendrite bridging is also likely to be formed to produce other internal defects, such a s air hole and solute enrichment in the residual molten steel located in the bridging area.