In this paper following topics will be discussed:1. Definition of organic reefs and the associated terms;2. Classification of reefs and their verious schems;3. Stages of reef growth;4. Cyclothem of forming various reefs during the Phanerozoic;5. Diagenetic processes of ancient reefs and their potentiality of reservoir for oil and gas. Then the paper briefly descripted three types of the Permiam reefs developed in southwestern China. These are (a) Jintianba reefs which are regarded as carbonate platform margin-reefs;(b)Baffling mounds or buildups which are irregularly spread on carbonate platform of east Sichuan and west Hubei;and (c)Sponge-algal reefs which are well developed in east Yunnan

southwestern Guizhou and northwestern Guangxi.