Abstract: Based on a moving boundary approach, a three-dimensional dynamic model is built for 2400 mm ~400 mm wide-thick slab molds by using ProCAST to realize the coupling simulation of flow field, temperature field and stress field. The results show that the position of the lower recirculation zone moves to the slab center by the effect of the solidified shell, which reflects the real flow condition of molten steel in the continuous casting mold. The liquid on the free surface flows from the narrow surface to the nozzle, the velocity increases first and then decreases, and the maximum velocity is about 0.21 m·s^-1, which occurs at 0.7 m from the nozzle. The center of the narrow face shell at the mold exit is the thinnest and increases from the center to both sides gradually, and the minimum thickness is about 10.4 mm. The wide face shell influenced by water flow impact grows more Unifornl than the narrow face, the wide face shell thickness near the corner is 18.9 ram, and the center thickness is 27.6 mm. The stress change trend of the slab shell is almost consistent with temperature, demonstrating that the initial solidified shell stress is mainly thermal stress. The effective stresses on the wide face and narrow face rise along the drop direction of mold height, and the maximum stresses of the slab corner, wide faee center and narrow face center are about 200, 100 and 25 MPa, respectively.