Abstract: This study addresses defects such as cold shuts, flow marks, porosity, and oxide inclusions that are prone to occur during the casting of a new type of gasoline engine piston integrated with a ring insert, internal cooling, and lightweight design. Three types of gating systems—nail, bottom, and side gating—were systematically designed and simulated. Through multi-physics coupling simulations including filling, solidification, and defect prediction using MAGMA software, the results indicate that the side gating system performs optimally in terms of molten aluminum flow stability, mold cavity filling completeness, and defect control. It exhibits uniform flow velocity and low turbulence, effectively reducing gas entrainment and re-oxidation. Hot spot analysis and solidification sequence analysis further confirm its good feeding capacity, with shrinkage defects mainly concentrated in the riser area, consistent with the principle of directional solidification. The research demonstrates that combining numerical simulation technology with gating system design and optimization can significantly improve the casting quality and production efficiency of complex-structure pistons, offering substantial engineering application value.