Abstract: It is known that the shape of the growth interface, the temperature, oxygen concentration distribution are sensitive to the magnetic field strength. In this paper, a low Reynolds number model was used for the simulation of a 200 mm large diameter silicon crystal growth under a vertical magnetic field with different strength, the Hartmann number is equal to 0, 500, 1000 and 2000 respectively. Numerical results showed that a vertical magnetic field can effectively reduce the strength of the flow at the radial orientation; and can reduce the flow at the meridian plane; the oxygen concentration is also decreased at the axial orientation. The isotherm becomes flat. However, when the vertical magnetic field strength is too higher, the oxygen concentration at the axial orientation and the turbulence intensity increased.