Abstract: The karsts of the middle Caledonian and the early Hercynian are widespread in Aiding area of Tahe oilfield in Tarim basin. Of which multi?karst and cavity system were formed by three episodic rising movements of the middle Caledonian. So the reservoir of the Ordovician in this area is dominated by fracture?cavity reservoir rocks, and characterized by north?south zonation in plane and oil bearing on the whole, being remained ancient oil reservoirs with ultra?thick or ultra?heavy oil. The macroscopic analysis and microscopic characteristics show that the hydrocarbon accumulation in Aiding area was earlier, and after reservoir?forming in the late Caledonian to the early Hercynian, it entered into the process dominated by late adjustment and reconstruction