Improving the thermal stability of silica (SiO2) aerogel plays a crucial role in expanding its heat insulation application. In this work, heat treatment in argon atmosphere was adopted to avoid the thermal oxidative decomposition of hydrophobic groups, which inevitably occurred in the heat treatment in air atmosphere. Also, the physicochemical properties were analyzed. The results show that the hydrophobicity of SiO2 aerogels still maintains at a contact angle of 140° after heat treatment in argon atmosphere at 700 ℃. In the differential scanning calorimetry test in air atmosphere, the peak temperature in exothermic reaction (Tpeak) of heat treated SiO2 aerogels reaches 584 ℃, which is approximately 300 ℃ higher than that of untreated SiO2 aerogels, thus improving the thermal stability. The results obtained also indicate that hydrophobic SiO2 aerogels could be used at high temperatures due to the improved thermal stability and safety.