Fluids are varied and complex in physical property due to greatly different longitudal and lateral distribution of the fluids in Ordovician reservoirs in Tahe Oil Field, Tarim Basin. It is shown that the early hydrocarbon accumula-tion and placement and the later charging and adjustment are the main mechanism of forming the Ordovician reservoirs in this field. The sealing condition of cap rock is the important control factor. The local lateral blocking of compact limestone and controlling of large faults are the cause of regional differentiation in hydrocarbon property and reservoir types. Correspondingly independent fracture-cavity system and multi-phased hydrocarbon accumulation lead the fluids greatly different in plane and vertical extent. Hydrocarbon is generally lighter in the upper and heavier in the lower of the reservoirs, and it is commonly lighter in the south and the east of the field and it is heavier in the north and the west. The depth of bottom water is evidently different in every fracture-cavity system because of the trap evolvement and the dynamic condition.