This study investigates the fracture surface morphological characteristics and permeability characteristics of sandstones with different particle sizes (siltstone, fine-, medium-, and coarse-grained sandstone). The research employs three-dimensional (3D) scanning tests and seepage characteristic tests to analyze the differences in morphological characteristics and seepage laws among the different lithologies. The results show that siltstone and fine-grained sandstone exhibit significant undulations and variations in elevation, while medium- and coarse-grained sandstone have more uniform distributions and less undulation. The Forchheimer formula is well-suited for describing the seepage characteristics of siltstone and fine-grained sandstone, whereas the Izbash formula is more appropriate for medium- and coarse-grained sandstone. The study also finds that the permeability characteristics of rock samples are influenced by both cleavage fractures and internal fractures within the matrix, with cleavage fractures being more sensitive to external stress. The findings provide valuable insights into the relationship between rock seepage and lithology, offering a basis for further research on the seepage law of rocks with different lithologies.This study investigates the fracture surface morphological characteristics and permeability characteristics of sandstones with different particle sizes (siltstone, fine-, medium-, and coarse-grained sandstone). The research employs three-dimensional (3D) scanning tests and seepage characteristic tests to analyze the differences in morphological characteristics and seepage laws among the different lithologies. The results show that siltstone and fine-grained sandstone exhibit significant undulations and variations in elevation, while medium- and coarse-grained sandstone have more uniform distributions and less undulation. The Forchheimer formula is well-suited for describing the seepage characteristics of siltstone and fine-grained sandstone, whereas the Izbash formula is more appropriate for medium- and coarse-grained sandstone. The study also finds that the permeability characteristics of rock samples are influenced by both cleavage fractures and internal fractures within the matrix, with cleavage fractures being more sensitive to external stress. The findings provide valuable insights into the relationship between rock seepage and lithology, offering a basis for further research on the seepage law of rocks with different lithologies.