Abstract: Cell wall of treacheary elements in some trees does not collapse as the cellular-water migrates to the extracellular ice during freezing, thus negative pressure comes up in cells. Negative pressure induce cavitation, and it results in embolism. Therefore, water transport is blocked in trees. Development of cavitation and embolism is regarded as the result of freeze_thaw cycles or of ice sublimation in some tissues when temperature rises fast after freezing. Root pressure forms again during vernal season, and cavitation and embolismare repaired in part. So water transport in trees isn't blocked too. Freezing stress results a great injury of trees in high latitude and some areas of mid_ high latitude. Cavitation and embolism in xylem treacheary elements are a kind of injury induced by freezing stress, and also the main reason that result in growth declines or death of trees. The paper reviews the causes of formation of cavitation and embolism, its mechanism and repair.