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.