The existence of —OH in the heavy oxide glasses leads to enormous loss in mid-infrared region due to worsening optical properties. Thus, removal of water in glass especially for mid- infrared application is a critical step. The effect of hydroxyl groups on the optical, spectroscopic and the optical fiber properties of the mid- infrared heavy metal oxide glass is discussed, the widely used dehydration techniques in recent years(reaction atmosphere process, budding dry gas, fluoride dehydration, chloride dehydration, etc.) are reviewed,their dehydration effects and the research progress are presented, and the status and the development direction of dehydration techniques in mid-infrared heavy oxide glasses are summarized.