To study the pore structure characteristics of middle-high rank coals (MHRC), five different kinds of coal samples from northern China were selected and pulverized, and the pore volume, pore size distribution, and fractal dimension were analyzed using N-2/CO2 adsorption and mercury intrusion porosimetry. The results show that the nanopores size of MHRC tends to decrease with the increase of coal rank, especially the ultra-micropores dominate in semi-anthracite coal. In addition, the fractal dimensions of the adsorption pore (pores >0.5 nm and pores <0.5 nm) are calculated, respectively. Both of these fractal dimension-fitting curves exhibit a U-shaped parabolic relationship with the R-o. It can be found that the nanopores is affected by the coalification jumps by analyzing the relationship between the pore structure parameters and R-o. The third coalification jump has a turning effect on the micropores development, and the fifth coalification jump significantly promoted the mesopores volume. (C) 2019 Elsevier B.V. All rights reserved.