Abstract: The carbonates of Ordovician are the principal reservoirs in Tahe oilfield,Tarim Basin.The diagenesis of Ordovician carbonates is characterized by multiple stages,different types and enviroments.The major diagenesis includes cementation,solution,fracture and hydrothermal diagenesis which controlled the evolution of reservoirs.The history of dagenesis and porosity evolution and the origin of formation of the Ordovician reservoirs were reconverted.