The　gradation　of　aggregate　and　the　hydration　reaction　of　cementitious　materials　are　important　factors　affecting　the　performance　of　backfill　materials.　Steel　slag　powder　(SSP)　can　be　used　as　both　aggregate　and　cementitious　material　according　to　different　particle　size.　SSP　has　multiple　influencing　effects　on　coarse　tailings　cemented　backfill　(CTCB).　Experiment　with　different　content　SSP　in　the　CTCB　was　designed.　And　uniaxial　compression,　nuclear　magnetic　resonance　and　scanning　electron　microscopy　techniques　were　used　to　characterize　its　macro　and　micro　characteristics.　The　relationship　model　of　aggregate　characteristics　on　strength　and　porosity　was　established　by　analyzing　the　characteristics　of　aggregate　using　gradation　and　fractal.　The　conclusions　mainly　include:　(1)　SSP　plays　three　main　roles　in　the　CTCB:　optimizing　the　gradation,　generating　hydration　reaction　and　influencing　the　hydration　reaction　of　cement.　(2)　There　are　good　gradation　and　fractal　characteristics　between　SSP　and　coarse　tailings,　with　a　grading　index　of　0.30-0.61　and　a　fractal　dimension　of　2.12-2.61.　(3)　The　relationship　between　strength,　porosity　and　gradation,　fractal　dimension　was　quadratic　function　relation,　and　then　the　grading　index　and　fractal　dimension　for　optimal　strength　and　pore　characteristics　are　0.45-0.49　and　2.33-2.40　respectively.