Supernumerary Robotic Arms (SuperLimb) are new types of wearable robots designed for human operation augmentation by working closely with the human limb. As a special collaborator of the wearer, the probability of accidental collision is greatly increased, thus posing a formidable challenge to the safety of humans. To address this issue, this paper proposes a sensorless interaction method based on dynamic parameter identification greatly increases the security guarantee between human and SuperLimb. To improve the identification accuracy of the dynamic system, a novel dynamic identification model considering the flexible elastic deformation of tendons is first derived. Subsequently, the detailed excitation trajectory design and optimization are presented. Then, the identification experiment is conducted on the SuperLimb. The experiment results show that the proposed approach with considering the influence of tendon can improve the accuracy of model estimation and the identified dynamic parameters are accurate. Finally, the application experiment is successfully applied in the human-SuperLimb system indicating that the proposed method is useful for increasing the security guarantee between human and SuperLimb.