Abstract: The Ordovician carbonate reservoirs with fractures and cavities in Tahe oilfield is characterized by serious heterogeneity, great changes of reservoir space, complex oil?water relations. Some wells drilled into the water zones procuce oil after high backflow volume. By means of experiences of searching gas by drainage process in Sichuan basin, it is recognized that the searching oil by drainage process can be practicable in Tahe Ordovician carbonate reservoirs. From the successful test, the process is optimized by selection of non?production wells with certain reservoir space, weak water energy, better logging data, oil flowers or H2S in testing. The successful practice of searching oil by drainage process in Tahe Ordovician carbonate reservoirs has deepened the recognition of hydrocarbon accumulation in such a reservoir, opening a new way for developing the carbonate reservoirs in Tarim basin