During the continuous casting of medium carbon steelMedium carbon steel, longitudinal cracks often occur, primarily caused by uneven heat transferHeat transfer in slag filmSlag film at meniscus between the mold and shellShell. This study investigated the heat transferHeat transfer behavior of the slag filmSlag film at meniscus using a mold simulator technique. The results showed that the slag filmSlag film thickness exhibit an initial decrease followed by a subsequent increase along the casting direction. Additionally, the total mold/shellShell thermal resistance Rtot, solid slag filmSlag film thermal resistance Rs, liquid slag filmSlag film thermal resistance Rl, interfacial thermal resistance Rint all appear an initial decrease followed by a subsequent increase along the casting direction. Overall, Rtot is 12.72 × 10−4 m2 K/W at the location of shellShell tip, and decrease to the minimum value 7.78 × 10−4 m2 K/W at 5 mm below the shellShell tip, then it begins to increase and finally is 9.68 × 10−4 m2 K/W at 10 mm below the shellShell tip.