Abstract: This study targets the cross-rolling piercing process of high-grade thick-walled steel pipes. It constructs thermo-mechanical coupling and plug temperature analysis models, and builds a 3D finite element model based on the Mannesmann piercing principle. The temperature field is solved using the finite difference method and Thomas algorithm via relevant control equations. Results indicate that the plug tip temperature exceeds 1200 °C, aggravating thermal fatigue wear. The black scale oxide film can lower the surface temperature, and the SiO₂ - containing molten layer provides key lubrication. Rotational speed impacts frictional heat and metal flow. High speeds increase the flow velocity difference between inner and outer layers, causing uneven wall thickness.