The　ultra　supercritical　boiler　technology　with　double　reheat　can　significantly　increase　the　efficiency　of　a　Rankine　cycle　power　plant,　and　reduce　fuel　consumption　for　a　given　output.　Recently　China　is　developing　1000MW　ultra　supercritical　boiler　with　double　reheat　which　is　arranged　in　tower　type　and　the　steam　parameters　are　350bar,　605oC/613oC/613oC.　Thermal-hydraulic　analysis　is　the　key　factors　for　the　design　and　operation　of　ultra　supercritical　boiler　with　double　reheat.　According　to　the　boiler　structure　and　furnace-sided　heat　flux,　the　water　wall　of　an　ultra　supercritical　tower　boiler　with　double　reheat　is　treated　in　this　paper　as　a　flow　network　system　consisting　of　series-parallel　loops,　pressure　grids　and　connecting　tubes.　Based　on　the　mass,　momentum　and　energy　conservations　and　some　supplementary　equations,　a　mathematical　model　is　developed.　Pressure　drop,　mass　flux　distribution,　outlet　vapor　temperatures　and　metal　temperatures　data　in　the　water　wall　at　BMCR　(boiler　maximum　continuous　rating),　75%　THA　(turbine　heat　acceptance)　and　30%　THA　load　are　obtained　by　iteratively　solving　the　mathematical　model.　The　results　show　that　the　water　wall　in　the　ultra　supercritical　boiler　can　operate　safely.　©　2015　The　Japan　Society　of　Mechanical　Engineers.