The design parameters of cementitious materials mixture ratio of nano ultra-high strength and high-flow concrete were proposed by orthogonal test, and the influence of nano-SiO₂ on the strength and workability of traditional ultra-high strength cement-based material doped silica fume and fly ash was studied. Same water-binder ratio, the concrete mix proportion test was carried out. Afterwards, the effect and mechanism of nano-SiO₂ on the compressive strength of concrete were explored. The results indicated that the optimum ratio of cementitious material in ultra-high strength and high-flow concrete is:nano-SiO₂:silica fume:fly ash:cement=1:8:20:71. In the range of 600~1 000 kg/m³, its fluidity has increased with increase of cementitious material, the compressive strength first increases and then decreases, with the maximum compressive strength of cementitious material of 800 kg/m³. It is concluded that the ternary multiscale stacking system formed by nano-SiO₂, silica fume and fly ash can optimize the compaction effect of powder materials in concrete micro-aggregates. Additionally, the secondary reaction of hydration reaction of nano-SiO₂ also improves the micro-structure of hardened cement stone and optimizes its morphology distribution, further increased its strength.