Abstract: Based on a series of SEM images of soil,the apparent porosity and fractal dimension were calculated,the influences of threshold,analyzing size,scanning position and magnification on quantitative analysis results of soil microstructure were investigated,and their affecting mechanism were discussed.It was found that the pore structure parameters obtained at relative low threshold value were close to the real soil fabric.Relative high threshold value was necessary and reasonable when the morphological characters of soil particles were analyzed.Magnification played an important role in analyzing the microstructure of soil by using scanning electron microscope(SEM),and a reasonable magnification should be chosen on the basis of research subject and purpose.According to the obtained results,some useful threshold values and magnifications were recommended.The suggestions and comments related to testing,observing,and image analyzing techniques during scanning process were given.It was significant for obtaining real and objective microstructure parameters by using SEM.