A multicomponent two-phase model was established to describe the macro/micro-transportation and the freckle formation during solidification, and the dynamic mesh algorithm was applied to perform the filling process during the vacuum arc remelting (VAR). Firstly, the thermodynamic calculation approach was used to evaluate the liquid composition with the variation of solid fraction during solidification, and the interdendritic liquid density of multicomponent alloys was obtained. Then, the freckle formed during the horizontal directional solidification was simulated and compared with the experiment one to study the freckle formation mechanism and influence factor. Finally, the developed model was used to investigate the influence of process parameters on the freckle formation in the industrial-scale VAR casting. Results show that the element composition has a significant effect on the density change of liquid phase during the solidification. The freckle forms with a high thermosolutal convection strength. The growth direction of freckles is determined by the liquid density difference and the angle between solidified interface and gravity direction. It is also found that the molten pool profile is affected by the electrode melting rate and cooling rate during VAR.