The coal-associated mud shale is widely developed in the east of the Qinshui Basin and has great potential for shale gas resources. Research on the pore structure characteristics of mud shale in this area is of great significance for the evaluation of shale gas-bearing properties and the realization of joint exploration and co-production of coalbed methane and shale gas. In this paper, the mud shale of the Permian Shanxi Formation from Well Y in the Wuxiang block of the basin was taken as the research object. The pore structure characteristics and fractal characteristics of the mud shale were studied by means of XRD, high-pressure mercury intrusion, and low-temperature liquid nitrogen adsorption. The results show that the mineral composition of the mud shale of the Shanxi Formation in the Y-well is dominated by clay minerals and quartz. There are a large number of pores smaller than 50 nm, and the pore structure is mainly composed of crack pores and "thin bottleneck" pores. The mud shale adsorption curve is of inverted S-type, suggesting type Ⅱ curve of Brunauer classification scheme. The desorption line belongs to the H2 type (both H1 type and H3 type) in the IUPAC classification scheme, and belongs to the B type (both E type and C type) in the De Boer classification scheme. The fractal dimension of mud shale in Shanxi Formation of Well Y is close to 3, and the heterogeneity is strong. Mineral composition, total pore volume, average pore size and TOC content are important factors affecting the fractal dimension of mud shale.