Abstract: In order to investigate the porous medium property and fractal characteristics of coal, Xishan coal field in Qinshui basin, Shanxi province is taken as the study object.The scanning electron microscopy(SEM) is adopted to analyze the pore strcutue characteristics on coal surface.Based on the SEM images, the pore fractal dimension of various coal samples is obtained through the box-counting method.Meanwhile, the influencing factors of fractal dimension are also analyzed.The research results show that coal surafe has the obvious fractal feature, and the complexity of coal pore structure can be well descibed by fractal theory.The value of fractal dimension ranges from 1.33 to 1.92 for different coal samples.Coalification, water content, burial depth and Protodyakonov's coefficient(f) have significant impact on fractal dimension of coal pore.As the R_o increase of and burial depth, coal surface tends to be rough and complex, leading to the increase of fractal dimension.However, the existence of water and ash content enables the coal surface to become relatively smooth, consequently, the value of fractal dimension is reduced.Fractal dimension is an effective parameter to evaluate the complexity of coal pore.In the field practice of gas control, attention should be paid to the coal with high fractal dimension.This coal is likely damaged severely, and it has strong gas adsorption property.The bad pore connectivity is not benefitical for gas extraction, which can results in the occurance of coal and gas outburst, gas emission, etc.during coal mining.