Abstract: In order to indicate the structure properties of the coal porosity quantitatively, three different coal rank samples, including lignite, bituminous coal and ant hracite, were selected to break into three different granularity, and the mercury porosimetry test was then performed. Based on the Menger sponge model and the therm odynamic model, the experimental data were processed to study the fractal characteristics of coal porosity. The results showed that the curves obtained from the Meng er sponge model did not fit the linear relationship.The curve was divided into two segments. The fractal dimension value DMof the front segment was greater than 3, an d the linear ftting degree of the back segment was too low. When the thermodynamic model was used to analyze the fractal characteristics of the pore, the curves show ed a significant linear relationship, and the ftting degree was more than 0.98. Meanwhile, the fractal dimension DTwas between 2 and 3.It was shown that the thermody namic model was more suitable for studying the fractal characteristics of the coal porosity than Menger sponge model. DTdecreased with the decrease of the coal partic le size, and the coal particle size had lttle effect on it. DTdecreased with the increase of coal rank, and the reason was analyzed from the viewpoint of the coal metamo rphism.