Abstract: In order to eliminate the low mechanical property and brittle character of SiO₂ aerogel, the cellulose nanofibrils (CNF) were used to reinforce SiO₂ aerogel through in-situ sol-gel process.The chemical structure, morphology, mechanical and physical properties of SiO₂ aerogels were characterized and analyzed.The improvement of mechanical properties and mechanism of SiO₂ aerogel reinforced with CNF were investigated. The results show that the CNF of unique nano network structure can enhance the bonding strength between SiO₂ particles. The appearance of Si-OH (960 cm^-1) and Si-O-Si (1 225 cm^-1, 1 056 cm^-1 and 800 cm^-1) characteristic absorption peaks represent the formation of stable chemical bond between cellulose and SiO₂. The all CNF of different content can significantly improve the mechanical properties of SiO₂ aerogel, and still remain SiO₂ aerogel itself light mass, high porosity and high specific area. When the CNF mass fraction is 6wt%, the SiO₂ aerogel reinforced with CNF has the best mechanical properties; its compressive modulus and strength are 12.43 MPa and 2.59 MPa, respectively.