In the numerical simulation of mold filling process, the calculation efficiency has been a key point for practical applications due to the complexity and thin-section of die castings. In current research work, a fractional step method was applied in the solution of the unsteady Navier-Stokes equations, which can be implemented with a single solution to the momentum/pressure equations at each time step. This method may avoid the decrease in efficiency induced by iteration. A water analog system was designed and developed to simulate the die casting process. The flow patterns were recorded by a high speed camera with a capturing rate of 500 frames per second. The simulation results were consistent with the experimental ones. Besides, the fluid flow patterns of several components were simulated by the fractional step and VOF algorithm, and the SOLA-VOF algorithm respectively. The simulation results showed that the combination of the fractional step method and VOF method can improve the computational efficiency to some extent in numerical simulation of mold filling process.