A model was established based on Maxwells equations and Navier-Stokes equations to numerically simulate the electromagnetic field and flow field in a rectangular mold with sectional aspect ratio of 5:1.The FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed for the model to execute the modeling,meshing,load applying and solving.The Ti-Al alloy melt was selected to illustrate and validate the effects of the harmonic field frequency on the distribution of the physical fields in the mold.The simulated results demonstrate that with an increasing frequency the electric current forms an ellipsoid cavity where it becomes much weaker,and that the melt flows more intensely with low frequency (less than 5 kHz) than with high frequency (more than 5 kHz).The melt is pinched from the central part in the mold to bipolar parts in which it forms two vortexes in each side.The maximum value of fluid velocity exists near the bipolar zone.