Abstract: According to the palaeontologic fossils, lithologic and electrie properties, the Middle-Upper Ordovician in Tazhong area can be divided, from top to bottom, into Sangtamu formation(Upper Ordovician) and Lianglitager formation (Middle Ordovician) which can be subdivided into limestone member with muddy intercalation, pure limestone member and muddy limestone member. They are of good comparable behavior in the whole area. Hence it is considered that in Middle-Upper Ordovician of Tazhong area obviously exists lithostratigraphic diachroneity and synchronous aniso-facies phenomena which is in lack of and unconformity contact with Lower Ordovician.

Key words: Tarim basin, Middle, Middle Ordovician, Late Ordovician, Regional stratigraphic correlation