Abstract: Widespread in East China is a suite of well-developed and very thick carbonate formations(from Sinian to Triassic).In the present paper a brief discussion has been gieven to one of the characteristic features of the early evolution of organic matter in carbonate rocks——the great diagenetic loss of organic matter and its bearing on the evalution of oil and gas prospects in carbonate rock-distributed areas.The authors have also described the characteristic features of the evolution of organic matter,such as gaseous hydrocarbons,souble organic matter and kerogen in the carbonate rocks which have evidently reached the late stage of organic evolution,as well as the highest temperature range they once underwent during their evolution history.In terms of the vertical distribution patterns of oil and gas.in the region of South Sichuan,the lowest limit has been prelimarily established for the commercial preservation of oil and gas in carbonate formations.