Abstract：The Tahe oilfield in the northern part of the Tarim basin is China’s first largest Paleozoic oilfield. It was discovered from 1990 to 1997. By 2002 a petroleum-bearing area of ~ 1000 km2 was controlled, with explored reserves of 250 million tons. Its discovery has great significance for guiding the search for this type of oilfield in the Tarim basin and even the whole of China. The author thinks that sediments in the Tarim oilfield are depression-type marine carbonate rocks in the ancient cratonic basin. It is located in a cratonic paleo-uplift-Shaya uplift, where faults and regional unconformities are very well developed, which are favorable for the concentration of oil and gas. As it adjoins the Manjiar oil-generating depression on the south, it is a good vector area for oil and gas migration. Two Hercynian tectonic movements resulted in the development of Ordovician paleokarst, thus giving rise to reservoirs with good pores, caves and fissures. Moreover, the occurrence of four phases of oil and gas migration and accumulation is the basic condition for the formation of a large oil/gas field. This oilfield is expected to become an exceedingly large oilfield with oil reserves of 800 million to 1 billion tons.