Water　wall　design　is　a　key　issue　for　an　ultra　supercritical　boiler.　In　order　to　increase　the　steam-water　mixture　turbulization　and　to　prevent　the　burnout　of　tubes　walls,　vertical　rifled　tubes　are　applied　in　Yuhuan　power　plant　boiler　which　is　the　first　1000　MW　ultra　supercritical　boiler　in　China　and　began　to　operate　in　December　2006.　Mathematical　modeling　and　thermal-hydraulic　analysis　are　key　factors　for　the　successful　design　and　operation　of　water　walls.　The　water　wall　system　is　treated　in　this　paper　as　a　network　consisting　of　circuits.　pressure　grids　and　connecting　tubes.　The　mathematical　model　for　predicting　the　mass　flux　distribution　and　metal　temperature　in　water　wall　is　based　on　the　mass,　momentum　and　energy　conservation　equations.　An　experiment　on　the　heat　transfer　characteristics　of　vertical　rifled　tube　was　conducted　with　the　aim　to　obtain　the　heat　transfer　performance　and　corresponding　empirical　correlations.　The　fitting　computational　formulas　are　applied　in　the　mathematical　model.　The　presented　modeling　method　is　more　accurate　than　the　conventional　graphic　method　and　can　be　applied　to　complex　circuit　structures.　The　mass　flux　distribution　and　the　metal　temperature　in　the　water　wall　are　calculated　at　35%.　50%　and　100%　of　the　boiler　maximum　continuous　rating　(BMCR).　The　results　show　a　good　agreement　with　the　plant　data.　The　maximum　relative　difference　between　the　calculated　mass　flux　and　the　plant　data　is　9.7%　at　50%　BMCR　load.　The　metal　temperature　difference　in　the　tip　of　fins　in　lower　circuit　8　is　about　3-7　degrees　C　at　35%　BMCR　load.　The　results　show　that　the　vertical　water　wall　in　the　ultra　supercritical　boiler　of　Yuhuan　power　plant　can　operate　safely.　(C)　2008　Elsevier　Ltd.　All　rights　reserved.