It is experimentally investigated by glancing angle X-ray diffraction (GAXRD) that the phase transition temperature and structure parameters of surface layer and differing from those of bulk layer in polycrystalline PbTiO3 ferroelectric thin film. The polycrystalline ferro-electric thin film is phenomenologically treated as a double layers structure: the surface layer is characterized as fine crystalline and low stressed, the bulk layer is characterized as large crystalline and high stressed. According to the influences of size and stress effects, the feature of phase transition of PbTiO3 polycrystalline ferroelectric thin film is described.