Abstract: Studies on soil microstructure are the front edge of the subject on soil mechanics and soil properties.However,the quantitative studies on the orientation characteristics of soil grains in the soil microstructural images(SEM) are an intractable subject in the past decades.An analytical method called the standard deviational ellipse method,which is often used for point set distribution analysis in geographical information system(GIS),is introduced for quantitative analysis of soil grains.Through the conversion and processing of soil microstructural images,the orientation angles of soil grains’ can be fast determined by using the standard deviational ellipse method,and the correlative data can be statistically analyzed,and then the characteristic of the soil grain orientation distribution can be obtained.The results show that the method is more scientific,objective and reliable for the quantitative studies on soil grain orientation distribution.