Many kinds of well-crystallized nanometer or submicron Ti-based perovskite ceramic powders were already synthesized successfully by sol-hydrothermal method at lower temperatures.In this paper,the analyses from X-ray diffractometry(XRD) and infrared spectra(IR) of products at the different stage during the process of PbTiO_3 synthesis reveal the primary mechanism of sol-hydrothermal method: sol treatment shortens the distance of reaction diffusion and promote the hydrothermal reaction.The sol-hydrothermal method can be used the preparation of many sub-micron,nanometer ceramic powders due to its lower synthesis temperature,so studies on its mechanism should avail the development of nano-powders synthesis technology.