Pore structure is one of the key factors that influence the dewatering, burning and conversion of lignite. In this study, the pore structure variation and fractal dimension of Shengli lignite in the drying process (150 - 500 degrees C) were investigated. The pore structure of lignite samples, including specific surface area, average pore diameter and pore shape etc., were obtained by N-2 adsorption/desorption at 77 K. And two fractal dimensions D-1 and 132 were calculated using the Frenkel-Halsey-Hill(FHH) method at relative pressures of 0 to 0.5 and 0.5 to 0.95, respectively. The results show that the general pore structure oflignite samples varies slightly in the drying process. Mesopores are mainly the open cylindrical pores and cracks pores, and micropores are mainly one dead end pores. The pore size distribution of mesopores is unimodal, and that of micropores appears to be multimodal. The variation trend of specific surface area is opposite to that of average pore diameter in the drying process. And before the drying temperature reaches 300 degrees C, the specific surface area, average pore diameter and mesopore volume show a "V" shape variation trend. The evolution mechanisms of pore structures during process mainly included moisture evaporated, pore shrinkage and decomposition of functional groups. The changes in D-1 were similar to those in specific surface area of mesopores development, reflecting the roughness of mesopore surface. The variation trend of D-2 and micropore volume tends to be the same, indicating the volumetric roughness of micropore. And the analysis of scanning electron microscope images of processed lignite, indicating that FHH modal is suitable to describe the pore structure change of lignite in the drying process. (C) 2016 Elsevier B.V. All rights reserved.