The second member of Xujiahe Formation in Xinchang area of western Sichuan is rich in natural gas resources, with large area of sandbody, low reservoir porosity and permeability, and complex genesis of sweet spot. It is of great significance to clarify the type and genesis of sweet spot in the second member of Xujiahe Formation in Xinchang area. Methods: Based on the analysis of reservoir petrology, pore throat characteristics and effective fracture characteristics, sweet spot is classified by core observation, thin section analysis, micro CT, cathodoluminescence and other technical means. Results: There are three types of sweet spot in the second member of Xujiahe Formation in Xinchang, including matrix pore type, fracture type and bedding fracture type. The causes of different types of sweet spot are different. High-energy distributary channels are formed under strong hydrodynamic conditions, quartz-rich sandstones are the basis for matrix-type sweet spot formation, and matrix-type are easily formed under relatively weak compaction, cementation and strong dissolution. It is easy to develop fracture-type in the matrix with good porosity and permeability near large faults; The distribution scale of bedding fracture type is small, there are differences in particle size and composition at different types of bedding interfaces, resulting in differential diagenesis process, forming a mechanical weak surface. Conclusions: The development of sweet spot is controlled by sedimentation, diagenesis and structural heterogeneity in Tx2 section in Xinchang area, . The genetic analysis of sweet spot type is conducive to the classification and evaluation of it.