The　secondary　flow　which　is　generated　by　the　angled　rib　is　one　of　the　key　factors　of　heat　transfer　enhancement　in　gas　turbine　blade　cooling　channels.　However,　the　current　studies　are　all　based　on　the　velocity　vector　and　streamline,　which　limit　the　research　on　the　detailed　micro-structure　of　secondary　flow.　In　order　to　make　further　targeted　optimization　on　the　flow　and　heat　transfer　in　the　cooling　channels　of　gas　turbine　blade,　it　is　necessary　to　firstly　investigate　the　generation,　interaction,　dissipation　and　the　influence　on　heat　transfer　of　secondary　flow　with　the　help　of　new　topological　method.　This　paper　reports　the　numerical　study　of　the　secondary　flow　and　the　effect　of　secondary　flow　on　heat　transfer　enhancement　in　rectangular　two-pass　channel　with　45　degrees　ribs.　Based　on　the　vortex　core　technology,　the　structure　of　secondary　flow　can　be　clearly　shown　and　studied.　The　results　showed　that　the　main　flow　secondary　flow　is　thrown　to　the　outer　side　wall　after　the　corner　due　to　the　centrifugal　force.　Then　it　is　weakened　in　the　second　pass　and　a　new　main　flow　secondary　flow　is　generated　at　the　same　time　near　the　opposite　side　wall　in　the　second　pass.　The　Nusselt　number　distribution　has　also　been　compared　with　the　secondary　flow　vortex　core　distribution.　The　results　shows　that　the　heat　transfer　strength　is　weakened　in　the　second　pass　due　to　the　interaction　between　the　old　main　flow　secondary　flow　and　the　new　one.　These　two　secondary　flows　are　in　opposite　rotation　direction,　which　reduces　the　disturbance　and　mass　transfer　strength　in　the　channel.