Abstract: It is defined that roundness of clastic particles is a degree of which are rounded in original edge angles.It is one of the important textural features and is usually used to indicate the textural maturity of clastic sediments.At present,the roundness is represented by a set of skeletons,which were designed by Powers in 1953.The skeletons show the rounded features from sharply angular to rounded particles.However,this method belongs to qualitative description.So it is necessary to determine the roundness quantitatively.In this paper,based on fractal theory and computer technology the procession of automatic statistics and calculations of particles fractal dimensions has been realized by box-counting method.The results show that the fractal dimensions can be considered as a quantitative index of describing the roundness of clastic particles.