To study the pore structure and fractal characteristics of add-treated coal, in this paper, the low-temperature nitrogen adsorption method, scanning electron microscopy and the fractal theory were used to analyze the coal samples. The results show that the acid treatment enlarged the wedge-shaped hole into a cylindrical hole. Under the influence of HNO3, the ash, volatile and sulfur contents are negatively correlated with the fractal dimension of the pore surface (D-1) and positively correlated with the fractal dimension of the pore structure (D-2). And the specific surface area and total pore volume of the coal samples are positively correlated with D-1 and negatively correlated with D-2 after acid treatment. Influenced by the specific surface area and total pore volume, the relationship between the fractal dimension and adsorption is consistent with the relationship between the fractal dimension and specific surface area/total pore volume. (C) 2020 Elsevier B.V. All rights reserved.