<p>When using manipulator to grasp and assemble thin and fragile components, they are prone to breakage due to factors such as the morphology error of the workpiece. In response to this issue, a cantilevered assembly robotic arm with dual passive compliance is proposed. Firstly, the operational process of the robotic arm grasping the fragile precursor ring for synthetic diamond synthesis is introduced, analyzing potential errors during assembly. Guidelines for designing a robotic arm structure with dual passive compliance are proposed, and the design process of the key component of the robotic arm, the compliant ring, is detailed. Secondly, to investigate the response of the robotic arm during operation, a 3D model of the robotic arm is constructed and imported into ADAMS software for simulation analysis, obtaining stress on the workpiece and forces and deformations on the compliant ring during the assembly process. Simulation results indicate that when there is a pose deviation between the thin and fragile component and the mating die, the designed robotic arm structure can adjust its gripping pose through adaptive deformation and successfully complete the assembly. Finally, a corresponding experimental prototype of the robotic arm is designed and manufactured for practical assembly experiments, demonstrating the correctness of the research results.</p>