Abstract: Carbonate reservoir is controlled by the late diagenesis and structural transformation, depositional environment has a certain impact to the carbonate reservoir , Even the development of carbonate reservoirs are not related to depositional environment directly, Especially in older chronologic age, mainly in cracks or fractured reservoir or paleokarst-formed fractured-vuggy reservoir, etc. Based on the research on characteristics of sedimentary rocks, this paper analyzed the the features and diagenesis of ancient Karst, divived the Akekule Paleokarstification exposure into three stages as freshwater karst, shallow burial mix of water and deep buried karst, which play an active role to the research of Tahe oilfield 4 Ordovician open platform carbonate rock weathering crust of fractured reservoir.