Silica aerogels were synthesized from hybrid silicon sources of TEOS and acid silica sol by two-step sol-gel method and supercritical drying. Different chemical compositions of the starting solution were altered in order to make an insight into the relationship between process parameters and the microstructural characteristics of resulting silica aerogels. The results indicate that a certain amount of acid silica sol may promote the gelation process while excessive nano-scaled silica particles easily result in dense structure and low specific surface area. The gelation time increases with the increasing water amount. Excessive water will lead to weak network structure of silica gels and thus larger shrinkage and lower porosity of the resulting silica aerogels.