The　growth　of　a　300mm　large　diameter　single　crystal　silicon　is　one　of　the　active　branches　in　silicon　material　research　and　production.　It　is　known　from　experiments　that　the　shape　of　the　growth　interface,　the　temperature　distribution　in　the　melt　etc.　are　sensitive　to　the　melt　motion.　However　it　is　quite　difficult　to　experimentally　visualize　the　convection　of　melt,　temperature　and　oxygen　field.　Thus　it　is　extremely　difficult　to　quantitatively　determine　how　melt　motion　influence　the　quality　of　crystal　by　experiments.　Numerical　simulations　can　provide　detailed　information　of　melt　motion,　distribution　of　temperature　and　so　on,　which　can　guide　the　growth　of　silicon.　In　this　paper,　a　low　Reynolds　number　K　-　epsilon　model　was　used　for　the　simulation　of　a　300mm　large　diameter　silicon　crystal　growth.　The　velocity　field　and　temperature　field　with　and　without　a　cusp　magnetic　field　were　visualized.　Through　this　study　how　a　cusp　magnetic　field　influences　the　melt　convection　was　clarified.