The various mechanisms of drought tolerance in plants has been reviewed in this paper. According to ways of responsing on drought stress, three primary types of drought tolerance in plants have been identified: (1) drought escape; (2) drought tolerance of dehydration postonement with high tissue water potential; (3) drought tolerance of dehydration tolerance with low tissue water potential. Drought escaping plants, known as desert ephemerals, are of the ability of completing their life cycle before a seriou...