TiO2 nanoparticles were prepared by sol-gel method，and were annealed at different temperatures from 300 to 800℃. Their interfacial and fractal characteristics as well as and phase transition were investigated by using synchrotron radiation SAXS and XRD techniques. The change of nanoparticle size with annealing temperature was determined. The relationship between the interfacial characteristics and phase transition was discussed in this paper.