The charcoal-permian system is a set of sea-land interconnection coal-bearing systems constructed in DaCheng District, Hebei Province. In order to study the organic geochemistry and physical characteristics of shale gas reservoirs, the type, abundance, maturity, mineralogical characteristics, porosity, permeability and gas-bearing properties of the reservoir were analyzed using dark mudstone samples from Shanxi-Taiyuan Formation in the study area. The results showed that the study area Taiyuan group organic matter type III, TOC value averaged 2.60%, Ro in 0.8% ~ 1.3% in the favorable stage. The Shanxi group was dominated by organic matter types III and II, with a TOC average of 2.30% and Ro of 0.7% to 1.2%, and the maturity was similar to that of the Taiyuan group, which was in the active and favorable stage. The clay mineral content of the Shanxi-Taiyuan group was generally higher than the brittle mineral content, with an average clay mineral content of about 57% and brittle mineral content of about 43%. Large clay mineral content helped to increase the content of adsorbed gas; brittle minerals were greater than 40%, which had positive implications for later fracturing yield enhancement measures. The pore volume of dark mudstone in the Shanxi-Taiyuan Formation averaged 0.0150 cm3/g, with an average specific surface area of 6.726 m2/g. The porosity ranged from 2.134% to 5.764%, with an average of 4.303%, and the permeability was generally less than 0.1 mD. The depth of mudstone buried in the Shanxi-Taiyuan Formation in the study area was moderate, and the physical characteristics of the reservoir were good, with conditions for shale gas storage. However, the penetration rate was low, requiring late production enhancement measures. The results of the research could provide a reference for shale gas development in large urban areas.