In this study, the molten steel flow inside the mold according to the shape change of the submerged entry nozzle (SEN) was simulated in the continuous casting process, and the effects of the immersion depth and long side length of the mold on the molten steel flow were compared and analyzed. The heat flow analysis was performed using the ANSYS Fluent software, and the turbulence model used the standard k-ε model. Based on the analysis results, the meniscus velocity decreased with deeper immersion depth, but it was slightly faster with lower immersion depth. In addition, the flow velocity of the molten steel of the outlet was increased because the molten steel exiting the upper outlet spread directly without colliding with the short side of the mold when the long side of the mold length was increased.