Computer simulation packages have had success in predicting filling behavior in extremely complicated geometries. However, most of the current numerical implementation is based on a hybrid finite-element/finite-difference solution with the middle-plane mode. This kind of model leads to some inconvenience in applications. Instead of using the middle-plane as the datum plane, the surfaces of the cavity are used as datum planes in this article. Additional boundary conditions in the gapwise direction are employed to keep the flows in the surfaces at the same section coordinative. Comparisons with experimental results obtained with an instrumented test mold and C-Mold results show good agreement in terms of pressure traces and melt-front advancement. It is demonstrated that the present formulation is well suited to handle cavities generated directly by current CAD systems.