Abstract: In order to study the pore structure characteristics of coal after acidification, the pore structure and mineral content of natural and acidified coal samples of high rank coal were measured based on low field nuclear magnetic resonance technology and X-ray diffraction experiment, and according to fractal theory, the fractal dimension of pores of two coal samples was compared and the acidification principle was discussed. The results show that the micropores and transition pores account for a large proportion in both natural and acidified coal samples; after acidification, the porosity of coal sample increases, and the minimum pore size and maximum pore size become larger; acidification can increase the pore volume and increase the uncertainty of pore type; the structure of macropores in two kinds of coal samples has fractal characteristics, and the fractal dimension of macropores increases after acidification; the mineral content of coal sample decreases after acidification, resulting in the change of pore structure.