Abstract：The diagenetic manner and evolution stage as well as the corresponding geological products and geochemical characteristics of REE, carbon, oxygen and strontium stable isotopes of Xekar Middle Ordovician Organic Reef-beach facies reservoirs were comprehensively studied in this paper. According to the “hydrological system”, the Middle Ordovician organic reef-beach facies strata were divided into four diagenetic systems, i.e., pore water, atmosphere water, temperature-pressure water and oilfield brines. The source and property of fluid flow and the interaction process between fluid and rock of each diagenetic system were different from each other, and their effects on the reservoir development were varied. Therefore, the diagenetic systems and manners closely related to the reservoir development mainly include the role of the karstification of atmospheric water at the ancient epigenetic stage, the role of temperature-pressure water and oilfield brines at the re-burial diagenetic stage, and the role of tectonic disruption at the middle-late re-burial diagenetic stage.