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, due to the complex formation mechanism of bedding- parallel fractures, it is difficult to accurately evaluate their impact on shale gas. This study takes the shale from the Wufeng- Longmaxi formations in the southern 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. Bedding- parallel fractures of the Wufeng- Longmaxi formations in the southern Sichuan basin are well- developed, mostly filled with striped calcite and quartz minerals. Bedding- parallel fractures contain three important microstructures, namely crack- seal bands, inclusion trails, and elongate crystals. The number of crack- seal bands can indicate the times of fracture opening. The inclusion trails can track the opening trajectory of fracture. According to the different driving forces of fracture opening during the formation of veins, bedding- parallel fracture veins can be divided into three types: fluid overpressure type, tectonic compression type, and tectonic- fluid overpressure type. During the growth of bedding fractures, they can serve as lateral migration channels for shale gas, which is helpful for the migration of shale gas to higher parts of the structure. The contact surface between the vein and the host rock is a mechanical weak surface which have a significant impact on the hydraulic fracturing effect.