Coal　gasification　slag　(GS)　is　a　potential　pozzolanic　industrial　waste　discharged　during　coal　gasification.　The　study　aimed　to　investigate　the　effect　of　finely　ground　GS　powder　on　the　fluidity,　rheology　and　viscoelasticity　properties　of　cement　paste,　which　is　essential　for　utilizing　GS　as　a　supplementary　cementitious　material　for　building　materials.　The　research　revealed　that　the　morphology,　physical　filling　effect,　and　particle　size　distribution　of　GS　powder　played　a　vital　role　in　the　workability　of　cement.　The　particle　size　distribution　of　the　GS-cement　system　followed　the　Rosin-Rammler　distribution　model,　and　the　width　of　the　particle　size　distribution　negatively　correlated　with　paste　fluidity.　The　rheological　characteristics　of　blended　paste　transitioned　from　Bingham　to　modified　Bingham　fluid　with　increased　GS　powder　content,　showing　shear　thinning.　Plastic　viscosity　can　predict　the　fluidity　and　thixotropy　of　the　paste.　GS　powder　at　10%　content　broadened　the　particle　size　distribution,　improved　fluidity　and　rheological　properties,　with　minimal　effect　on　viscoelastic　characteristics.　With　increased　GS　powder　content,　plastic　viscosity,　yield　stress,　and　thixotropy　of　blended　paste　increased　continuously,　resulting　in　a　slow　transition　from　viscosity　to　elastic　solid.　Extending　mechanical　grinding　time　improved　the　fineness　and　activity　of　GS　powder,　optimized　the　particle　size　distribution,　and　reduced　water　demand,　minimizing　negative　effects.