Abstract: Nano-SiO₂(NS) has very strong pozzolanic activity, nucleation effect and filling effect, so using nano-SiO₂ to improve the performance of cement-based materials has become a hot research topic of many scholars. This topic studied the effect of different dosage of NS on the strength and durability of lightweight aggregate concrete. The effects of NS on the macrostructure and microstructure of concrete were summarized and analyzed by testing the mechanical properties (compressive and flexural resistance) and chloride ion permeability of lightweight aggregate concrete, as well as the SEM and EDS test methods. The results show that NS can effectively improve the mechanical properties of lightweight aggregate concrete at appropriate dosage. The compressive strength and flexural strength of 28 d were 21.6% and 46.2% higher than that of the blank group concrete respectively. The results of chloride ion penetration show that the resistance to chloride ion permeability of lightweight aggregate concrete increases linearly with the increase of the content of nano-SiO₂. Concrete interface transition zone (ITZ) has also undergone significant changes, its thickness decreases, the morphology is also more dense. The ratio of calcium to silicon in ITZ decreases with the increase of the amount of NS, which indicates that the C-S-H gel of hydration product increases and Ca(OH)₂ is consumed in this region, resulting in a dense transition zone, which is conducive to the increase of the strength.