To reveal the underlying mechanism of the field synergy torsion screw in enhancing mixing and heat transfer performance, and to analyze the influence of pin-barrel on its performance, this study employed ANSYS Polyflow software to conduct numerical modeling and simulations of the field synergy torsion screw both before and after the addition of pin-barrels, with comparisons made against conventional single screws. Through flow field analysis, performance analysis, and synergy analysis, the mechanism by which the field synergy torsion screw enhances mixing and heat transfer was systematically investigated, and the impact of pin-barrels on its performance was further examined. The research results indicate that the field synergy torsion element in the field synergy torsion screw can force polymer melt to form a torsion-spiral flow, improve the synergistic effect between rubber material velocity field, velocity gradient field, and temperature gradient field, increase the stretching flow in the flow field, and enhance the convective heat transfer capability. After adding pin-barrel, the synergistic effect is further improved due to the diversion effect of the pin, and the mixing and heat transfer performance is further enhanced. However, the local temperature uniformity near the pin will be adversely affected.