The　accurate　calculation　and　analysis　of　hydrodynamic　characteristics　and　flow　instability　are　of　great　significance　for　the　optimal　design　and　safe　operation　of　the　water-cooled　wall　of　a　660　MW　ultra-supercritical　CFB　boiler.　Based　on　the　flow　network　system　method　and　the　conservation　equations　of　mass,　energy　and　momentum,　the　mathematical　model　of　thermal-hydraulic　calculation　was　established　and　the　thermal-hydraulic　characteristics　of　660MW　high-efficiency　ultra-supercritical　circulating　fluidized　bed　boiler　developed　by　China　at　four　loads　were　calculated　and　analyzed　with　this　model.　At　the　same　time,　a　one-　dimensional　single-channel　universal　numerical　calculation　model　for　flow　instability　analysis　of　ultra-supercritical　boilers　was　established　and　the　calculation　and　analysis　of　flow　instability　for　the　dangerous　circuit　was　carried　out.　The　results　show　that　the　total　system　pressure　of　the　water　wall　of　the　ultra-supercritical　CFB　boiler　is　lower　than　that　of　the　traditional　pulverized　coal　furnace;　positive　ow　characteristics　are　observed　in　the　water　wall　and　the　maximum　flow　deviation　among　the　four　loads　is　20.98%;　the　maximum　outlet　fluid　temperature　deviation　is　8.4,　occurring　on　the　rear　wall;　the　metal　temperature　of　the　water　wall　at　four　loads　are　both　permissible;　the　water　wall　will　not　flow　instability　and　the　operation　of　the　boiler　is　safe　and　reliable.　©　2020　Chin.　Soc.　for　Elec.　Eng.