Abstract: Based on the fractal geometry theory,according to the granulometry and infiltration test,the relation between the fractal dimension of grain composition and coefficient of non-uniformity was established from the grain composition and Darcy law.The physical meaning of the fractal dimension of grain composition was demon-strated by considering the complexity and irregularity of the granular structure of sandy soil.Furthermore,the rela-tion between the fractal dimension of grain composition and permeability coefficient was discussed by using linear regression analysis.The study shows that the better the grain composition is,the greater the coefficient of non-uniformity,the smaller both the fractal dimension and the permeability coefficient.The result indicates that the fractal dimension of the grain composition,which describes the permeability of sandy soil quantitatively and di-rectly,is an effective parameter for describing the size composition of sandy soil and its grain composition charac-teristics.As a result,this paper provides a new way for research on the permeability of the porous medium as well as the fractured porous medium.