The properties of silica sol, such as the interface characteristics and microstructure, were comparatively studied by small angle x-ray scattering (SAXS) assisted by dynamic light scattering. Four synthesis routes were adopted to relate the properties of silica sol with the synthesis situation. Very big difference of SAXS results was found between the base-catalyzed and the acid-catalyzed silica sols with ethanol used as solvent. Under the acid-catalysis of low molecule-weight organic acid, not only were polysiloxane macromolecules obtained, particle suspension of silica was also produced with complicated inner structures of particles. With ethanol or water as solvent, it was found that the silica particle would become more irregular in morphology with more polarity of solvent. The formation of Si-O tetrahedron was more difficult in the acidolysis of tetraethoxysilane by formic acid than in the other hydrolysis routes. An interesting co-existing of positive deviation and negative deviation from Porod's law was found in the silica sol with water solvent, and a detailed explanation has been given. Many nano-scaled structural difference among these different synthesis situations were revealed, which was difficult to be recognized by the experimental methods other than SAXS.