In this thesis, synchrotron radiation small angle X-ray scattering (SAXS) and Nano-CT were applied to detect the pore structure of two coal samples, and based on quartet structure generation set (QSGS) model, numerical simulation of methane adsorption-diffusion in these two samples was carried out; experiments of SAXS fractal determination and methane isothermal adsorption were carried out in three coal samples. The following conclusions were made: The pore diameter range detected by SAXS is 2 ~ 70 nm, which can approximately represent the mesopore characteristics. In this range, two samples exhibit similar unimodal pore size distribution and similar average pore diameters. The pore diameter range detected by Nano-CT is above 60 nm, mainly lying in 60 ~ 2000 nm, which can approximately represent the macropore characteristics. In this range, the pore and throat distribution statistics of these two samples show a similar variation trend. Both in the mesopore and macropore range, the sample with a smaller average pore diameter is of higher fractal dimension values. The numerical simulation in QSGS model visualized the dynamic process of methane adsorption-diffusion, and provided a good choice for further studying the impact of pore structure on gas adsorption and diffusion, and with the increase of the amount of adsorbed gas in different positions in the QSGS model, the pore gas pressure also increases. The surface fractal dimension and the pore fractal dimension calculated based on SAXS fractal theory show a positive correlation with the methane adsorption capacity and a negative correlation with the methane diffusion capacity.