In　order　to　prepare　ultra　high　toughness　cementitious　composites　(ultra　high　toughness　cementitious　composites,UHTCC),　the　dosage　of　fly　ash　and　quartz　sand　influence　of　the　mechanical　properties　of　PVA　fiber　reinforced　cementitious　composites　were　discussed,　based　on　the　compressive　test,　the　flexural　test,　the　direct　tensile　test　and　the　scanning　electron　microscope　(SEM)　test.　In　addition,　the　optimal　dosage　of　fly　ash-quartz　sand　by　mixing　of　fly　ash　and　quartz　sand　was　studied.　The　results　indicate　that　the　more　dosage　of　fly　ash,　the　less　compressive　strength　and　the　more　tensile　deformation　is.　However,　when　the　quality　of　fly　ash/the　quality　of　cement　(m　(FA)/m(C)　)is　greater　than　2.7,　the　tensile　deformation　increases　slowly.　When　the　quality　of　sand/the　quality　of　banding　material　(m(S)/m(B))　is　0.36,　the　tensile　deformation　performance　is　the　best.　The　research　shows　that　the　optimal　dosage　of　fly　ash-quartz　sand　system　is　m(FA)/m(C)　-m(S)/m(B):　1.2-0.48;　m(FA)/m(C)-m(S)/m(B):　2.2-0.36.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.