In order to reveal the mechanical properties and internal laws of rock and soil mass from a deeper perspective,many scholars have carried out researches on the pore structure of rock and soil mass. Electronic computed tomography (CT) is the most commonly used method for quantitative observation of pore structure of rock and soil mass in recent years. In this paper,CT scan images of clay soil,rock and foamed concrete were used to calculate the fractal dimension of pores by gray scale method and binarization method respectively,and the relationship between the porosity of rock and soil mass and the fractal dimension of pores was studied,and the characteristics and applicability of the two methods in the study of fractal characteristics of pore structure were compared and discussed. The results show that the treatment effect of binarization depends on the selection of threshold value,and the threshold value calculation method based on the original porosity of sample is simple and effective;However,the grayscale method preserves more original image information. For different geotechnical materials,the relationship between porosity and fractal dimension of pores obtained by binarization method is related to a good power function. When gray scale method is used,the fractal dimension of rock and soil mass presents a slight increase trend with the increase of its porosity,which is approximately linear. In general,the two treatment methods can be used to study the fractal characteristics of the pore structure of the rock and soil mass,but each has its advantages and disadvantages,and the appropriate method should be selected according to the research object.