Based on analyzing the character of infrared specrum of water in the sepiolite structure, this paper assigned every infrared band of structure hydroxyl (OH), water of crystallization (OH2) and zeolite water (H2O). In high frequency area (3700~300 cm-1),the Mg-OH stretchingabsorption bandνMg_OHis around 3 6 8 0 cm-1, the Al - OHstretching adsorpti bandνAl-OHis around 3625 cm-1, the stretching absorption bandνOH2 of crystal water OH2is around 3560 cm-1, the bandνH2Oof zeolite water and adsorption water H2O is around 3400~ 3500 cm-1, and the band around 3260 cm-1is the bandνH_boundof hydrogen bond among water. In middle frequency area (1700~1600 cm-1), the band around 1640~1600 cm-1is the bending vibration bandδH2Oof zeolite water and adsorption water, and band around 1615~1630 cm-1is the bending vibration bandδOH2of crystal water. In low frequency are (700~ 600 cm-1), the band around 690 cm-1is the librating bandρAl-OHof Al-OH, and the band around 642 cm-1is the librating bandρMg-OHof Mg-OH. Moreover, the authors have studied the difference in infrared spectra between hydrothermal sepiolite and sedimentary sepiolite, and found thatνMg-OHof hydrothermal sepiolite is stronger than that of sedimentary sepiolite, whileνAl-OHof hydrothermal sepiolite is weaker than that of sedimentary sepiolite. By analyzing infrared spectrum of heated sepiolite, it is found that the variation character of infrared specrum of heated sepiolite is consistent with the phase change. Finally, the authors point out that infrared spectrum of water in the sepiolite plays the role of indicating structural stability.