Abstract: Aim To find a new way of characterizing grafting ratio of polymeric surface, and study the relationship of retardency performance and grafting ratio.Methods ABS acted as materials for study, electron beam preirradiation was used to graft the monomer on the surface of polymer under the different conditions. Mass method and area method were used to indicate the grafting ratio, L OI was measured to study their relationship. Results The relation between mass grafting ratio and L OI was less linear. However, the relation between grafting ratio in area method and L OI was linear partly. Conclusion Using area method to indicate the grafting ratio of polymeric surface and is an important method for the flame retardancy of polymer.