The potential of a 3D FDM (Finite Difference Method) computer code was presented, in prediction of flow patterns by modeling the mold filling phenomena through different gating systems. In this code, improvements and modifications were made on the original SOLA VOF and Donor Acceptor algorithms. A more accurate solution procedure for handling free surfaces is developed in order to describe the flows through complicated gating designs. A block casting of 200?mm×200?mm×50?mm with two different gating designs was chosen as the verifying problem. Water analog studies are carried out on these two gating designs. The comparison indicates that computer simulation could be a powerful tool in shaping gating systems. The potential of a 3D FDM (Finite Difference Method) computer code was presented, in prediction of flow patterns by modeling the mold filling phenomena through different gating systems. In this code, improvements and modifications were made on the original SOLA VOF and Donor Acceptor algorithms . A more accurate solution procedure for handling free surfaces is developed in order to describe the flows through complicated gating designs. A block casting of 200? Mm × 200? Mm × 50? Mm with two different gating designs was chosen as the verifying problem. Water analog studies are carrying out on these two gating designs. The comparison indicates that computer simulation could be a powerful tool in shaping gating systems.