Respectively using pressed method and diffuse reflectance method, the infrared absorption spectrua of sorts of kaolin in various areas were obtained. The relationship between the structure characteristics of kaolin and its absorption peaks was analyzed. The results showed that compared with pressed method, the use of diffuse reflectance Fourier transform infrared spectroscopy, combined with the K-M function, results in corrected infrared spectra with high sensitivity and is more accurate and easier to analyze. Furthermore, based on a high frequency wave of 3 700~3 600 cm-1 sections of kaolinite-OH characteristic absorption peaks, the crystallinity of all kinds of kaolnite can be known quickly. The result is consistent with the Hinckley index surveyed by X-ray diffraction technique.