Abstract: In order to study the pore structure characteristics of middle rank coal reservoirs, we qualitatively and quantitatively analyzed the pore structure characteristics of 15 middle rank coal samples from different coal seams in 8 parameter wells in the Panguan syncline by scanning electron microscopy and high-pressure mercury pressure experiments, and quantified the pore fractal characteristics of different aperture segments based on the fractal theory, and discussed the relationship between fractal dimensions and vitrinite reflectance, as well as the inorganic composition of the coal, the pore structure parameters, the porosity discussed and the permeability. The results show that: there are mainly five types of microscopic pores in the middle rank coal of Longtan Formation in Panguan syncline; the pore morphology of the piezoelectric mercury curve is divided into three types; the seepage fractal dimensions are smaller than the diffusion fractal dimensions, and the comprehensive fractal dimensions mainly reflect the complexity of the diffusion pores; the seepage fractal dimensions are negatively correlated with the vitrinite reflectance, the ash, the mineral mass fraction, the porosity, the average pore size, the total pore volume, and the permeability, and positively correlated with the moisture; and the diffusion fractal dimensions are negatively correlated with the ash, the mineral mass fraction, the average pore size, and the total pore volume. The diffusion fractal dimension is negatively correlated with ash, mineral content, porosity, average pore size, total pore volume, and positively correlated with vitrinite reflectance, moisture, and total pore specific surface area.