Bedding-parallel fractures are widely developed in organic-rich shale, which are important reservoir space and lateral migration channel of shale gas, affecting the migration, enrichment, preservation of shale gas and the fracturing effect of reservoir. However, the formation of bedding-parallel fractures usually has multiple stages and causes, making the formation mechanism of bedding-parallel fracutures very complex and difficult to distinguish. This study takes the shale from the Wufeng-Longmaxi Formation in the Southeastern Sichuan Basin as an example. Based on field, core, thin section, and scanning electron microscopy data, the macroscopic characteristics of bedding-parallel fractures and the microstructure characteristics of filling veins were studied, and the formation mechanism of bedding-parallel fractures was analyzed. The results show that the surface of the unfilled bedding fractures is smooth and has obvious mirror features. The scratches and steps on the fracture surface can indicate the relative displacement direction of the surrounding rock on both sides of the fracture, and the fracture can extend several meters to tens of meters forward along the bedding plane. The bedding-parallel fractures are mostly filled with striped calcite and quartz minerals, with a width of 0.5cm~5cm. Bedding-parallel fractures contain three important microstructures, namely crack-seal bands, inclusion trails, and elongate crystals. The shape of the crack-seal band is controlled by the initial fracture, and the number of bands can indicate the times of fracture opening. The inclusion trails are parallel to the opening direction of the fracture and can track the opening trajectory of fracture. According to the different driving forces of fracture opening during the formation of veins, bedding-parallel fractures veins can be divided into three types: fluid overpressure type, tectonic compression type, and tectonic-fluid overpressure type. During the growth of bedding fractures and veins, they can serve as lateral migration channels for shale gas, affecting the enrichment and preservation of shale gas. And as mechanical weak surfaces, they have a significant impact on the hydraulic fracturing effect.