Abstract: In order to study the variation of pore characteristics of coal samples after modification with Fenton reagent and the influence on the permeability of coal, the T₂ relaxation time of different coal samples before and after modification with different Fenton reagent was obtained based on low field nuclear magnetic resonance （ＮＭＲ） experiments, according to the T₂ relaxation time spectrum, the variation of pore characteristics of Fenton modified coal rock was analyzed. Combined with the experiment of permeability measurement of coal samples, the mechanism of reaming and augmenting of coal samples by Fenton reagent modification was analyzed. The results show that the coal samples of different coal grades are treated with Fenton reagent, the micropores of coal samples develop and expand, the micropores and the macropores are interpenetrated with each other to form large-size pores, and even macroscopic small cracks are formed, and the permeability of the modified coal sample was significantly increased.