The　effects　of　the　coolant　flow　rates　on　the　thermal　and　flow　fields　of　the　first　two　intermediate　pressure　(IP)　stages　of　an　ultra-supercritical　steam　turbine　was　numerically　investigated　using　the　Conjugate　Heat　Transfer　(CHT)　method,　and　the　un-cooled　case　was　also　simulated　for　comparison.　The　threedimensional　Reynolds-Averaged　NaviereStokes　(RANS)　solution　was　utilized　to　analyze　the　flow　field　and　temperature　distributions　of　the　first　two　IP　stages.　The　numerical　results　show　that　the　steam　cooling　system　has　proved　its　ability　to　cool　down　the　high　temperature　components,　even　in　the　case　with　the　low　coolant　flow　rate.　The　cooling　performance　can　be　improved　with　increased　coolant　flow　rate,　however,　great　flow　losses　would　be　induced　and　make　the　stage　efficiency　reduce　by　1.23%.　The　different　coolant　flow　rates　also　lead　to　great　differences　in　the　flow　field　in　the　front　cavity　of　the　first　stage:　ingress　dominated　flow　condition　with　the　low　coolant　flow　rate　and　egress　dominated　flow　condition　with　the　high　coolant　flow　rate.　The　negative　influence　of　the　ingested　hot　main　steam　on　the　cooling　effect　was　also　described.　©　2013　Published　by　Elsevier　Ltd.