Air-staged　combustion　and　low-NOx　burner　retrofitting　are　commonly　adopted　for　reducing　the　formation　of　NOx　in　furnace　by　most　of　large-scale　coal-fired　units　with　ultra-low　pollution　emission.　However,　the　risk　of　slagging　and　high-temperature　corrosion　on　water-wall　tubes　which　are　exposed　in　a　strongly　reducing　atmosphere,　is　sharply　increased　when　the　unit　is　operated　under　low-NOx　combustion　condition.　Because　sulfur　and　ash　content　in　the　feeding　bituminous　coal　are　higher　and　different　from　that　of　the　designed　coal.　Some　corrosion　layer　and　deposits　adhered　on　water-wall　tubes　at　the　location　between　separated　over　fire　air　(SOFA)　nozzle　and　F　burner　level,　were　sampled　from　an　actual　boiler.　The　deposits　show　a　layered　structure　which　is　distinguished　by　its　color.　Each　layer　of　deposits　after　physically　detaching　was　characterized　by　X-Ray　fluorescence　spectrometer　(XRF)　and　X-Ray　diffraction　(XRD).　The　morphology　and　elemental　content　of　corrosion　layer　were　analyzed　by　Scanning　Electron　Microscope　(SEM)　instrument.　The　results　show　that　the　corrosion　layer　is　mainly　consisted　of　various　iron　sulfides　and　oxides,　and　PbS.　It　also　contains　minor　of　As,　Ge,　Ga,　Se　and　Zn　elements.　Fe,　S,　Zn　and　Pb　elements　are　enriched　in　the　innermost　and　middle　layers　of　deposits,　and　they　mainly　exist　as　FeS,　FeS2,　PbS,　ZnS　and　ZnAl1.04S2.13.　However,　Pb　element　is　found　only　in　the　innermost　of　deposits.　The　outermost　layer　of　deposits　contains　large　amounts　of　aluminosilicates　and　aluminates,　minor　of　sulfides.　The　Pb　and　Zn　enrichment　in　deposits　could　be　well　explained　via　the　reaction　pathway　that　is　the　gaseous　Pb　and　Zn　colliding　with　high　H2S　concentration　giving　birth　to　gaseous　ZnS　and　PbS.　Theses　gaseous　sulfides　are　transported　to　the　surface　of　water-wall　tubes　via　condensation　and　thermophoresis　deposition.　Enrichments　of　Zn　and　Pb　in　deposits　are　about　three　to　four　orders　of　magnitude　higher　than　that　of　Zn　and　Pb　in　raw　coal,　which　would　be　an　index　for　evaluating　the　sulfide　corrosion　behavior　of　water-wall　tubes.　©　2020　Chin.　Soc.　for　Elec.　Eng.