Tarim Basin is an important district in China’s oil and gas exploration and production, but so far, there is inadequate understanding of the carbonate fissure system of the Tahe oilfield, which has seriously impaired exploration and development of this oilfield. As we have stduied, the fissure system of the Tahe oilfield in its Ordovician carbonate reservoir is very complex. Basically there are two types: tectonic fissures, and stylolites. Many predecessors considered that the former is vital and often ignore the latter, whereas we think the latter is more important than the former. Stylolites are widely developed within the Ordovician carbonate reservoirs of the Tahe oilfield, and tectonic fissures can not be matched with the stylolites in terms of frequency or their relationship with oil. According to the relationship between stylolites and bedding, stylolites in the Ordovician carbonate reservoirs of the Tahe oilfield can be divided into three kinds: bedparallel stylolites, tilted stylolites, and vertical stylolites. These three kinds are associated and form complex network systems which constitute the primary internal hydrocarbon migration passages within the reservoir. At the same time, together with the fissures, they construct an effective hydrocarbon migration channel and a weak structural plane that can create favorable conditions for both hydrocarbon accumulation and subsequent development.