Abstract: Combining low-temperature nitrogen gas adsorption and scanning electron microscopy (SEM) to investigate the effects of microwave irradiation on pore structures and surface topography of lignite. The use of these techniques allows us to determine the specific surface area, pore volume, average pore size, pore shape and surface topography. It is concluded that with the increase of microwave irradiation time or power, fractal dimension values and average pore size decreased gradually; specific surface area and pore volume decreased remarkably and then increased slightly; the surface of coal sample tended to be smooth and the pore holes shrank.