©　2016,　Editorial　Department　of　Chinese　Society　of　Power　Engineering.　All　right　reserved.The　effect　of　shaft　seal　leakage　on　intermediate-pressure　(IP)　first-stage　steam　cooling　performance　of　an　ultra-supercritical　high　&　intermediate　pressure　(HIP)　combined　steam　turbine　was　numerically　investigated　by　coupled　flow-field　calculation　and　conjugated　heat-transfer　method,　while　the　steam　cooling　characteristics　were　analyzed　and　compared　respectively　under　no　steam　cooling,　steam　cooling　and　leakage　steam　cooling　conditions.　Results　show　that　turbine　stage　efficiency　at　first　stage　of　IP　cylinder　decreases　with　the　rise　of　shaft　leakage　flow　rate;　for　a　shaft　leakage　flow　rate　of　9.68　kg/s,　the　turbine　stage　efficiency　would　be　decreased　by　0.68%　in　comparison　with　the　zero　leakage　case;　the　cooling　mechanism　of　leakage　steam　on　the　first-stage　components　is　same　as　that　of　the　cooling　steam,　and　their　cooling　effects　are　different　due　to　their　different　flow　rates　and　temperatures;　compared　with　the　steam　cooling　condition,　the　cooling　effect　on　blade　root　by　steam　mixture　from　both　shaft　leakage　and　coolant　flow　weakens　with　the　rise　of　leakage　flow　rate,　resulting　in　increased　temperature　but　reduced　temperature　gradient　at　blade　root.