The side sealing technology is crucial for ensuring the quality and process stability in twin‐roll casting (TRC). Investigating the temperature and stress distribution in side dams under operational conditions is vital, especially in understanding the causes of side dam fractures. Optimal performance of side dam materials is achieved when the boron nitride (BN) matrix is fine and homogeneous, with zirconium dioxide (ZrO2) and silicon carbide (SiC) particles evenly dispersed throughout. The fracture of the side dam after casting is mainly caused by BN interlamellar tear. The coexistence of BN lamellar tearing and BN layer fracture leads to the fracture of the side dam during the casting process. Through finite element simulation, the effects of variables such as pouring temperature, preheating temperature, and side dam thickness on temperature and stress distribution were analyzed. The findings indicate that a preheating temperature range of 1200–1300 °C minimizes thermal stress in the side dam. Building on these findings, a composite structure for the side dam is developed. Both internal and external composite structures have shown significant effectiveness in reducing thermal stress. These results are pivotal in extending the service life of side dams and enhancing the stability of the TRC process.