Wellbore instability of horizontal wells in Qianfoya Formation in northeast Sichuan seriously restricts the efficient development of the continental shale oil and gas resources in Puguang Area. Analyzing hydration damage characteristics of Qianfoya continental shale is the important basis for revealing wellbore collapse mechanism and supporting wellbore stability. The underground core observation shows that a large number of organic-rich slickensides and interlayer structures are developed in Qianfoya continental shale in Puguang Area. Therefore, the continental shale samples with and without slickenside structures are selected as the research objects respectively. In this study, the characteristics of mineral composition, microstructure and chemical-physical properties of Qianfoya shale are analyzed. Furthermore, the hydration damage effects of different fluids (i.e. deionized water, white oil, oil-based drilling fluid and water-based drilling fluid) on meso-structure of Qianfoya shale with multitype weak planes are studied based on CT technology. In addition, the analysis and discussion about wellbore instability mechanism of Qianfoya shale in Puguang are conducted based on the developed wellbore stability model considering the influence of multi-type weak-plane structures. The results show that: (1) The Qianfoya continental shale in Puguang Area is mainly composed of quartz and clay minerals (nearly 60%) which is dominated by illite and chlorite. The micro fractures parallel to the bedding plane are well developed in Qianfoya shale with the wettability of water-wet and oil-wet. And the overall hydration dispersion of shale is relatively weak. (2) The hydration damage characteristics of shales immersed in deionized water and water-based drilling fluid are obvious. On the contrary, the hydration damage effects of white oil and oil-based drilling fluid on meso-structure of shale samples with and without organic-rich slickensides are not obvious. It indicates that the oil-based drilling fluid has good performance in hydration inhibition and there is no obvious organic matter dissolution in the shale with multi-type weak planes. To a certain extent, it can be concluded that the physicochemical interaction between oil-based drilling fluid and Qianfoya shale is not the main factor leading to the wellbore collapse. (3) Ignoring the characteristics of multi-type weak-plane structures in Qianfoya shale will underestimate wellbore collapse pressure and result in an increased risk of horizontal wells instability. The research results deepen the understanding of the hydration damage characteristics and wellbore instability mechanism of Qianfoya continental shale in Puguang Area and provide theoretical support for the horizontal well construction in Qianfoya shale formation.