The pore structure of different metamorphic coal was analyzed by mercury intrusion porosimetry and N-2 adsorption. Combined with the fractal dimension models of the Frenkel-Halsey-Hill and Menger, the pore size range of the experiment was spliced reasonably. A new pore classification scheme is put forward by fractal dimensions, revealing the pore structure and fractal characteristics of different metamorphic coal. The results suggest that pores exhibit piecewise fractal characteristics. A new pore classification scheme is put forward by piecewise fractal dimensions: I(0-2.0 nm, corresponding to D-1); II (2.0-50 nm, corresponding to D-2); III (50-2000 nm, corresponding to D-3): IV (2000-20,000 nm, corresponding to D-4); V (>20,000 nm, corresponding to D-5). It is not inconsistent with the international union of pure and applied chemistry for pore classification, which shows that the new pore classification scheme is reliable. (C) 2019 Elsevier B.V. All rights reserved.