Abstract: 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.