In this paper, the structure of diatomite was studied systematically, it was found that there was jointed hydroxyl groups in Zhejiang white soil, only isolated and adjacent hydroxyl groups were found in other diatomite. There were still Si-O and Al-O vibrations verified by IR in the diatomite. Acid washing and roast all could change pore size, pore size distribution and structure. Upon roasting, its structure varied, free water disappeared and bound water decreased. When roasted at 1150℃, the amorphous silica of which diatomite is composed crystallized into α-cristobalite. Except Jiling diatomite had primary pores, Yunnan diatomite had thirdary pores, and all the others had secondary pores.

Key words: DIATOMITE, PORE SIZE, SILICON DIOXIDE, PORE SIZE DISTRIBUTION