Thermal-hydraulic　performance　of　water　wall　system　is　a　key　operating　target　for　supercritical　once-through　boiler.　In　this　paper,　the　water　wall　system　of　a　600　MW　supercritical　circulating　fluidized　bed　(CFB)　boiler　with　complex　furnace　structure　is　treated　as　a　simplified　series-parallel　flow　network,　which　consists　of　parallel　flow　loops,　pressure　nodes　and　connecting　tubes.　Based　on　the　mass,　momentum　and　energy　conservation　of　these　components,　a　complex　but　accurate　mathematical　model　for　predicting　the　thermal-hydraulic　characteristics　of　boiler　heating　surface　is　developed,　which　introduces　numerous　empirical　correlations　for　heat　transfer　and　flow　resistance.　The　model　was　iteratively　solved　using　the　quasi-Newton　method,　and　the　thermal-hydraulic　parameters　of　the　water　wall　system　at　different　operating　loads,　including　mass　flux　distribution,　total　pressure　drops,　outlet　vapor　temperature　and　metal　temperature　profiles　are　obtained.　The　results　exhibit　good　flow　distribution　characteristics　and　low　mass　flux　deviations　in　the　water　wall　system,　and　the　total　pressure　drop　is　far　lower　than　that　in　conventional　supercritical　once-through　boilers　at　different　operating　loads.　It　is　also　found　that　the　outlet　vapor　temperatures　and　the　temperature　differences　in　the　water　wall　system　are　all　in　a　permissible　range　and　the　metal　temperatures　meet　the　boiler　operating　requirement　completely.　It　implies　the　design　of　water　wall　system　in　supercritical　CFB　boiler　is　successful.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.