The influence of Nano-SiO2 (NS) on the strength of high-performance concrete (W/B=0.24, W/B=0.29, W/B=0.34) has been studied in this paper. The results show that compressive strengths of concrete in both the early and later stage can be improved by adding Nano-SiO2 content. And the influence on the early compressive strength is greater than that on the later compressive strength. According to the results, 3%-5% Nano-SiO2can be used as the proper mixing ratio. X-ray diffraction, SEM (scanning electron microscope) and mercury injection experiment were used to analyze the action principle of Nano-SiO2 microscopically, the microscopic characteristics of concrete can be significantly improved through interfacial and filling effect effects so that the performance of concrete can be accordingly improved.