Abstract: Based on the fractal geometry method for studying low-temperature nitrogen adsorption, the pore structures and fractal characteristics of organic-rich coal measures shale in continental Yan'an Formation and sea-land transitional Taiyuan Formation at the northeastern margin of Ordos Basin are studied in this study. The fractal FHH model is used to calculate the fractal dimensions D₁ and D₂ of the large pores (4.34-100 nm) and small pores (less than 4.34 nm), so as to comparatively analyze the relationship between pore structure parameters and fractal dimensions as well as the influences of TOC and mineral compositions on the both. The results are as below:(1) In Yan'an Formation, pore sizes are distributed in the range of 1.8-59 nm, showing a "bimodal" pattern; ink-bottle, slit and plate-like pores are dominantly developed. In Taiyuan Formation, pore sizes are ranged in 3-4.5 nm, showing a "unimodal" pattern; ink-bottle pores are mainly developed. (2) Coal measures shale has double fractal characteristics. D₁ and D₂ are positively correlated, and D₁ is larger than D₂, indicating the more complex structures of large pores. Besides, the spatial structures of two types of pores in Yan'an Formation are all complex, while those of large pores in Taiyuan Formation are very complex, but small pores have strong heterogeneity. (3) The smaller the average pore size of coal measures shale is, the more the small pores will be, the larger the specific surface area will be, the bigger the total pore volume will be, and the higher the fractal dimension will be, i.e., the more complex the pore structure is, the more irregular the pore surface will be. The D₁ and D₂ of Yan'an Formation and D₂ of Taiyuan Formation can reflect the corresponding pore structure characteristics, respectively. (4) The pore structure parameters and fractal dimensions of Taiyuan Formation are more significantly affected by TOC and mineral compositions than those of Yan'an Formation. (5) As compared with Taiyuan Formation, Yan'an Formation has better shale reservoir, and is more favorable for the adsorption, occurrence, diffusion and flow of coal measures shale gas.