The　rotor　system＇s　dynamic　stability　of　high-parameters　steam　turbine　under　the　combined　action　of　oil-film　force　and　labyrinth　seal　force　was　researched.　The　improved　two-control-volume　bulk-flow　model　was　used　to　compute　the　dynamic　coefficients　of　multi-stage　labyrinth　seals,　and　the　results　show　that　the　cross-stiffness　of　high　pressure　cylinder　shroud　seals　has　reached　about　107N/m,　which　is　equal　or　even　higher　than　the　six-pad　tilting　bearing＇s　cross-stiffness,　this　indicate　that　seal　is　the　dominant　factor　of　system＇s　dynamic　stability.　The　rotor　system　was　modeled　by　finite　element　method　and　then　the　rotor-bearing-seal　dynamic　model　was　built　to　calculate　the　influence　of　seal　clearance　and　rotating　speed　on　rotor　system　dynamic　performance,　the　analysis　results　indicate　that　the　logarithm　decrement　δmin)　of　the　rotor　system　decreased　rapidly　in　considering　of　the　sealing　force,　but　the　critical　speed　of　rotor　system　is　influenced　weakly,　while,　the　δminis　influenced　by　the　seal　clearance　regionally,　proper　choice　of　seal　clearance　in　range　of　0.5　mm　to　0.8　mm　which　is　less　than　the　design　clearance　(0.8mm),　can　optimize　the　leakage　and　stability　of　the　system.　The　concept　design　knowledge　representation　and　scheme　optimization　for　coupling　design　was　accomplished　by　axiomatic　design　(AD)theory,　which　takes　four　schemes　of　seal　design　as　the　case,　and　this　indicate　that　the　AD　method　is　simple　and　effective.　©　2013　Chinese　Society　for　Electrical　Engineering.