Abstract: Evaporite is an important rock type because of its economic value. In the earth's surficial water body, the easy-dissolved salts can deposit and form evaporite by evaporation, condensation and crystallization The research of evaporite theory has become to a special branch of science with the countinously discovery of evaporite deposits and the development of geophsics and geochemistry. In the past two to three decades, the theoritical research of evaporite reached its peak, accompany with the study of modern sedimentation, more and more new models of salt forming have been put forward and the classical ones had been surmounted, accompliented and modified, China is an evaporites devoloping country, the study of modern diagenesis of evaporite is the key to reveal the mechanics of palaeo-evaporite. The present paper, based on the stastics of modern saline lakes in Qinghai-Tibet Plateau, emphasized that the deep water body is one of the important material source of salt forming; suggested that the theoritical fundation of evaporite forming is the cyclation of natural water in salt-bearing basin, and the cy cle of saline water disslution is the key factor both in the study of diagenesis and catagenesis; disscused the evolution of hypersalin water, and especially emphasised the significance of dating and fluid enclusion of salt minerals. The world-wide spreaded models of salt forming in the past three decades and the generally domesticlly adopted models in the recent years are introduced brifly in this paper too. And the author believes that the theory of evaporite forming will certainly go to a new stage on basis of the evolutional study on evaporite.