In this paper，in order to study the influence mechanism of activator type on the performance of desulfurization gypsum alkali-activated slag tunnel fireproof coatings（DGAC），with alkali content of 4% and AAC content of 20%，the effect of activator type，namely CaO+Na₂CO₃，Ca（OH）₂+Na₂CO₃，CaO+Na₂SO₄，Ca（OH）₂+Na₂SO₄ and NaOH，corresponding to DGAC of CNC，CHNC，CNS，CHNS and NH respectively，on the drying time，setting time，dry density，compressive strength，water resistance，and fire resistance of DGAC was explored，and the influence mechanism was revealed by SEM and XRD. The results showed that the drying and setting time was CNS>CHNS>CNC>CHNC>NH；the compressive strength and water resistance wereCHNC>CNC>NH>CNS>CHNS，and CHNC generated more flocculent C-S-H gel，which intersectd tightly with needlelike AFt and had the best water resistance and compressive strength；the fire resistance was CHNS>CNS>NH>CHNC>CNC，and the lower alkalinity of the activator in CHNS and CNS，a small amount of C-S-H gel was generated，the morphology of calcite was coarser，and the overall structure of hydration products became loose，therefore CHNS and CNS had lower compressive strength，and better fire resistance.