Abstract: Based on the cryogenic nitrogen adsorption experiment, the pore structure in Xishanyao Formation low rank coal in Hoxtolgay Basin were analyzed from the morphologic character of nitrogen adsorption-desorption curve, the distribution curve of pore diameter and the FHH fractal feature. The relation between pore struct ure and quality of the low rank coal was investigated from the aspects of coal vitrinite reflectance, coal petrography-maceral and coal industry analysis. The results indi cate that the micropore and minipore are the primary pore types and the majority of them show typical shapes of“ink bottle' and open, only few are“one-closed end" por es. The pores are more complicated with the increasing of fractal dimension as well as BET specific surface area and pore volume, the decreasing of average pore dia meter. The pore volume and BET specific surface area of coal samples grow with the increasing of inertinite contents and decreasing of vitrinite content. Both the pore volume and BET show asymmetric“V" shape tendency with the mineral contents with the turning point at the 1% of mineral contents. Besides, the increasing of vitrinite 「 eflectance, moisture content and ash yield would decrease the pore volume and BET specific surface area of coal samples.