采用溶胶－凝胶（Ｓｏｌ－Ｇｅｌ）法在硅衬底上制备了ＰｂＴｉＯ３ 多晶薄膜，利用红外反射光谱测量了薄膜在室温下的声子谱，并首次观察到８ 个红外活性的声子模，分别位于８１、１５５、２０７、３００、３４４、４６０、５００ 和６２１ｃｍ － １，其中位于３００ 和４６０ｃｍ － １的两个声子模以前未曾见报道过．与单晶相比，除了位于１５５ｃｍ － １的声子模向高波数移动之外，其它的声子模均向低波数移动，并讨论了影响声子模移动的因素． PbTiO3 polycrystalline thin films were prepared on silicon substrate by Sol-Gel method. The phonon spectrum of the films was measured by infrared reflectance spectroscopy at room temperature. For the first time, eight infrared-active phonon modes , Located at 81, 155, 207, 300, 344, 460, 500 and 621 cm - 1, respectively, of which two phonon modes at 300 and 460 cm - 1 have not been previously reported. Compared with monocrystal, except for the phonon mode located at 155cm - 1, the other phonon modes shift to lower wavenumbers, and the factors affecting the phonon modes are also discussed.