Cellulose nanofibril (CNF) aerogels combine important properties of conventional silica aerogels with their own excellent biocompatibility and biodegradability, which could be applied in various fields. However, applications for cellulose aerogels have been limited by cellulose’s hygroscopicity. In order to improve the hydrophilicity and comprehensive properties of cellulose aerogels, the simple immersion method was used to introduce silica parties into the cellulose matrix to synthesis cellulose nanofibril/silica composite aerogels. The chemical structure of cellulose aerogel and composite aerogels was analyzed with Fourier transform infrared spectroscopy (FTIR). The microstructure of aerogels was observed by scanning electron microscope (SEM). The physical, mechanical properties and contact angle of aerogels were tested and analyzed. The results show that the peaks of —OH located at 3 340 cm-1 in composite aerogels were all weaker compared with cellulose aerogel, which indicates that the formation of Si-OH due to the introduction of silica and also lowered the hydrophilicity of cellulose aerogel. The appearance of the peaks of Si—CH3 and Si—O—Si represents the modification of trimethylchlorosilane (TMCS) and the formation of stable chemical bond between cellulose and silica particles. The silica content of the composite aerogels was affected by the immersion time, and in turn affected the density, BET surface area and porosity of aerogels. The composite aerogel had better comprehensive properties when immersed into silica sol for 10 min. It had homogeneous microstructure and hydrophobicity, with contact angle of 152°. It also had good mechanical properties and low density, the compressive modulus and strength of the composite aerogel were 591 and 138 MPa, respectively. Its density was only 01 g·cm-3.