The experimental results of changing heat treatment temperature on the microstructure and thermodynamic properties of hydrophobic silica aerogels are reported and discussed. Prepared with sodium silicate precursor, ethanol (EtOH)/ hexamethyldisiloxane (HMDSO) /hydrochloric acid (HCL) as solvent exchange and surface modification agent, the crack-free and high hydrophobic silica aerogel monoliths were obtained. Silica aerogels possessed the superior properties, such as low density (0.116 g/cm3), high surface area (871 m2/g), high hydrophobicity (~145°) and low thermal conductivity (0.025 W(m K)−1). Silica aerogel monoliths maintained hydrophobic behavior up to a maximum temperature of 460°C above which they become hydrophilic. After a thermal process changing from room temperature to 400°C, the final product was still remained hydrophobic (~125°) and presented good performance with surface area of 530 m2/g. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.025 to 0.049 W/ (m K) as temperature increased from 25 to 400°C, revealed an excellent heat insulation effect during thermal process.