Abstract: To investigate the effect of ash content on coal pore structure, the change laws of scattering curves and pore parameters of four low-volatile bituminous coal samples were quantitatively analyzed by small angle X-ray scattering (SAXS). The X-ray scattering data indicate that for all samples, the ash is mainly confined in the same size range of 1.0 nm^-1< scattering vector q < 2.0 nm^-1 corresponding to the pore size range of 3 nm to 6 nm. The positive deviation of SAXS data from Porod's law for all the test coal samples is observed. In comparison of original coal samples, the demineralised coal samples possess higher pore numbers, pore volume, pore specific surface area and pore surface fractal dimension. Additionally, the micropore volume increases associated with decreasing the most-probable and average pore diameter for demineralised coal samples. The results imply that SAXS can effectively characterize the pore distribution of coal.