The Lower Ordovician is composed mainly of a series of carbonate platform deposits interbedded with shale and is especially characterized by a large number of organic reefs or buildups that occur widely in the research area. The reefs have different thicknesses ranging from 0.5m to 11.5m and lengths varying from 1 m to 130 m, and the most important is that the reefs are characterized by a great quantity, wide distribution, thin thickness and small scale. The reef-building organisms are Archaeoscyphia, Recepthaculitids, Batostoma, Cyanobacteria, Pulchrilamina and so on. Through the study of the characteristics of the reef-bearing strata of the Lower Ordovician in the Yichang area, four sorts of Biofacies are recognized, which are (1) Shelly Biofacies: containing Tritoechia-Pelmatozans community and Tritoechia-Pamatotrema community; ( 2 ) Reef Biofacies: including Batostoma community, Calathium-Archaeoscyphia community, Pelmatozoans-Batostoma community, Archeoscyphia community and Calathium-Cyanobacteria community; ( 3 ) Standing-water Biofacies : including Acanthograptus-Dendrogptus community and Yichangopora community; and (4) Allochthonous Fades: containing Nanorthis-Psilocephlina taphocoense. The analysis of sea-level changes indicate that there are four cycles of sea-level change during the period when reef-bearing strata were formed in this area, and the development of reefs is obviously controlled by the velocity of sea-level changes and the growing velocity of accommodation space. The authors hold that reefs mostly formed in the period of high sea level. Because of the development of several subordinate cycles while the sea-level rising, the reefs are characterized by a great quantity, wide distribution, thin thickness and small scale. The research of evolution of community shows that succession and replacement are the main forms. The former is favourable to the development of reefs and the latter indicates the disappearance of reefs.