Abstract: In order to investigate the natural fracture development law and its influencing factors in deep-buried tight oil reservoirs, in this paper, we take the Ⅱ-Ⅵ tight oil formations of the third member of Paleogene Hetaoyuan Formation in southeast An'peng area of the Biyang Sag, Nanxiang Basin as an example. A systematic evaluation has been carried out based on a large number of core, thin section, physical properties, imaging, conventional logging and water flooding data. The Ⅱ-Ⅵ oil formations belongs to fan-delta front deposits with high content of rock debris, which are near-source deposits. There is a good positive correlation between reservoir porosity and permeability. For sandstone reservoirs with different lithologies, fractures are mainly developed in fine sandstone, followed by siltstone, but not in pebbled sandstone. In the target layer, high-angle and vertical fractures are dominant, accounting for 87.8%, while low-angle and horizontal fractures account for 7.3% and 4.9%, respectively. The main controlling factors for fracture development in tight reservoirs in the target formations include lithology, sedimentary microfacies and structural characteristics. Fractures are usually developed in single or composite sand bodies with thinner thickness and finer granularity. Fractures are mainly developed in front channel, the flank of channel, mouth bar and the outer edge of far sand bar body. However, fractures do not develop in sheet sand or front delta microfacies. In addition, fractures mainly develop at the transition end of structure, and mainly at the top and wing of forward structure. The fractures in the target strata are mainly distributed along the WE and NE directions, followed by NW direction. It is believed that the fractures were mainly formed in the Neogene depression period (late Himalaya). Fracture is an important factor leading to water channeling in tight oil reservoirs, so it is necessary to strengthen the dynamic and static monitoring of fracture development degree, expansion scale and direction.