Sulfur　dioxide　(SO2)　is　a　toxic　pollutant　and　its　fixation　is　a　high　cost　but　imperative　task　for　sulfide　metallurgy　industry.　Although　being　a　mature　technology　for　on-line　fixation　of　SO2　by　limestone　injection　in　coal-fired　boilers,　its　application　is　rarely　investigated　in　the　sulfide　metallurgy　plant.　Extending　this　technology　to　the　metallurgy　industry　is　highly　plausible,　but　with　the　feasibility　and　practicability　waiting　to　be　uncovered.　Herein,　feeding　CaO　into　the　rotary　volatilization　kiln　as　SO2-fixation　agent　is　demonstrated　to　be　an　efficient　in-furnace　desulfurization　strategy　for　zinc　smelting　plant.　The　sulfur　distribution　within　the　entire　smelting　process　is　systematically　analyzed,　determining　that　the　critical　procedure　for　pressuring　the　desulfurization　system　is　the　rotary　volatilization　kiln.　The　thermodynamics　analysis　shows　that　addition　of　CaO　is　feasible　for　SO2　fixation　by　forming　CaS　or　restraining　the　reductive　decomposition　of　SO42−.　The　industrial　tests,　including　the　online　monitoring　of　kiln　flue　gas　and　kiln　slag　analysis,　validate　the　thermodynamics　analysis,　realizing　a　24.6%　reduction　of　SO2　in　the　flue　gas　by　converting　gaseous　SO2　to　solid　CaS　via　feeding　20%　CaO.　The　present　study　highlights　an　effective　strategy　for　on-line　fixing　the　SO2,　being　a　potential　way　for　relieving　the　desulfurization　pressures　in　zinc　sulfide　metallurgy　plant.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.