Abstract: To investigate the effects of deacidifier particle size and usage concentration on the enrichment of heavy metals in municipal solid waste incineration (MSWI) fly ash, the study used ultrafine Ca(OH)₂ emulsion as a substitute for traditional hydrated lime powder. It compared the enrichment characteristics of heavy metals in fly ash from waste incineration flue gas purification systems under different dilution ratios. The heavy metal elements investigated included As, Cd, Pb, Cr, Cu, Ni, Zn, Hg, Ba, and Cr(VI), with a focus on analyzing their enrichment patterns in semi-dry flue gas deacidification towers and bag filters. The results showed that, compared to traditional hydrated lime powder, the use of ultrafine Ca(OH)₂ emulsion significantly increased the enrichment ratios of As, Cu, Zn, Se, and Ba by 0.4-2.7 times in the fly ash from semi-dry deacidification towers, while Cd and Pb increased by 7.0-8.4 times, and Hg by 44.7 times. Conversely, Cr, Ni, Ba, and Cr(VI) decreased by 52% to 89%, with a greater enrichment in bag filter fly ash, all showing a decreasing reduction trend as the dilution ratio increased. By optimizing physical properties and reaction efficiency, the ultrafine Ca(OH)₂ emulsion markedly altered the enrichment patterns of heavy metals in the flue gas purification system, facilitating the upstream enrichment and graded treatment of pollutants. The findings provide a scientific basis for the targeted regulation and resource-oriented management of heavy metals in waste incineration fly ash.