A 3D mathematical model was proposed to simulate the mold filling process in high-pressure die casting(HPDC) to improve accuracy considering the surface tension. Piecewise liner interface calculation(PLIC) and volume of fluid(VOF) methods were used to construct the pattern of the liquid interface. A coupled levelset and VOF method(CLSVOF) was proposed to capture the interface pattern and obtain its normal vector. A continuum surface force(CSF) model was used to consider the surface tension. Two water analogy experiments were carried out using the proposed model. Simulation and experimental results were analyzed and compared; and the effects of surface tension were also discussed. The simulation results agreed well with the experiments and the simulation accuracy was an improvement on interface geometries, liquid flows, and gas entrapments. A 3D mathematical model was proposed to simulate the mold filling process in high-pressure die casting (HPDC) to improve accuracy considering the surface tension. Piecewise liner interface calculation (PLIC) and volume of fluid (VOF) methods were used to construct the pattern A coupled levelset and VOF method (CLSVOF) was proposed to capture the interface pattern and obtain its normal vector. A continuum surface force (CSF) model was used to consider the surface tension. Two water analogy experiments were carried out using the proposed model. Simulation and experimental results were analyzed and compared; and the effects of surface tension were also discussed.