Low cost, impurity-free and low thermal conductivity Al
2O
3-SiO
2 composite aerogel were prepared from AlCl
3·6H
2O derived gel through ion exchange technology and sol-gel method by dipping silicon in tetraethyl orthosilicate (TEOS), subsequently surface modification and ambient pressure drying were employed. The effects of different organosilane modifiers on the structure and thermal insulation properties of the Al
2O
3-SiO
2 composite aerogels were explored. The results show that Al
2O
3-SiO
2 composite aerogel shows the most uniform microstructure in the neutral (pH=7) modified environment of trimethoxy methylsilane (MTMS). The SiO
2 and Al
2O
3 phases mainly exist in amorphous form. MTMS is more effective in reducing the -OH group on the surface of Al
2O
3-SiO
2 wet gel to form Si-O-Si and Al-O-Si groups. The specific surface area and pore volume of Al
2O
3-SiO
2 aerogels are as high as 574 m
2/g and 2.3 cm
3/g, respectively, and the thermal conductivity is as low as 0.029 W(m·K)
-1. The above research provides support for the application of aerogel materials in the field of thermal insulation.