Many　defects　of　single　crystals　are　caused　by　the　nonplanar　solidification　front.　The　transverse　temperature　gradient　at　melt-crystal　interface　results　in　nonplanar　solidification　fronts.　The　location　of　a　cast　in　the　directional　solidification　furnace　affects　heat　dissipation　and　thus　influences　the　transverse　temperature　gradient.　This　paper　presents　a　criterion　and　a　searching　algorithm　to　find　the　optimal　location　of　the　cast　for　flattening　the　solidification　front.　A　numerical　simulation　was　employed　for　the　verification　of　our　method.　Additionally,　the　effects　of　the　size　of　the　cooling　device　of　the　furnace　on　the　optimal　location,　the　transverse　temperature　gradient　and　the　solidification　time　were　discussed.　The　transverse　temperature　gradient　is　reduced　about　50%　without　increasing　much　solidification　time　when　setting　the　cast　with　a　varying　thickness　mould　at　the　optimal　location.　In　addition,　the　optimal　location　is　mainly　influenced　by　the　radius　of　the　cooling　ring.　(C)　2016　Elsevier　B.V.　All　rights　reserved.