Abstract: Air-staged combustion and low-NO_x burner retrofitting are commonly adopted for reducing the formation of NO_x 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-NO_x 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 detach ing 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 ZnAl_1.04S_2.13. 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.