Abstract: Generally, rolling is the primary form of bedload movement on pebble riverbeds under certain flow conditions. Due to different moving distances of the particles with different sizes on a bed surface, sorted sediment transport will occur, forming a stable structure with coarse particles as the main body of the bed. This work focused on a study of the coarsening process of non-uniform pebble beds during clear water scouring and the sorting modes that were stably formed after scouring. Based on a rolling mechanics model, tracking of the rolling particle movement under different conditions was numerically calculated; a gradation calculation model of stable non-uniform pebble beds washed by clear water was developed. This model was used in a practical example to calculate variations in bedload gradation and gradation curves at different time for different river sections. The theoretical results presented in this paper are applicable to rolling movement of pebbles and provide a theoretical method for further studies of pebble bed sorting.