Abstract: Micro-structure of coal samples from Datong coal mine and Tunliu coal mine were respectively detected using mercury intrusion method.According to cumulative porosity percentage of pores with various radius of coal，the pores with coal were classified into three categories，namely micro-pore，mesopore and macropore.Combined the calculation principle of fractal dimension of porous structure，the fractal dimensions of three types of pore were obtained by linear regression.The results showed that the fractal dimensions of different pore calculated by section linear regression were able to better describe the complex porous structure，where both fractal dimension of mesopore and macropore was more than that of micropore.It indicates that there exists inhomogeneous structure between mesopore and macropore，as well as obvious discreteness of pore distributed in the range from the mesopore to macropore.

Key words: Coal rock, Mercury intrusion, Fractal dimension