Lightweight design of orthodontic dental casts is critical for reducing the cost of invisible orthodontic treatments. In this study, deformation characteristics of actual dental casts were analyzed using the finite element method, and three structural infill strategies (hollow, honeycomb, and cube) were applied for weight reduction. Film lamination was simplified as a normal load applied to the outer surface, and the overall deformation response was used to evaluate lightweight performance. Finally, a newly fabricated dental cast was used to verify the simulation results. The findings indicate that the honeycomb infill structure provides the optimal lightweight effect for orthodontic dental casts, followed by cubic and hollow structures.