Light Emitting Diode (LED) sorting machine is high speed, high precision and high reliability equipment. Swing arm is the most impotent part of the machine. The dynamic characteristic of the high speed rotatable swing arm will directly influence the sorting of chip. Based on cantilever beam theory, the static stiffness and natural frequency of swing arm are the keys to its dynamic characteristics by analyzing the movement of the swinging arm. The static and dynamic characteristics of the different ply angles of swing arms were analyzed separately by the ANSYS software. The optimal ply angle was confirmed. In order to ensure the static stiffness and natural frequency of swing arm, the sizes of swing arm were optimized. The results show that ply angles do not affect the static and dynamic characteristics of swing arm. After the optimization design of swing arm, the weight is increased of 6.8%, the static stiffness is increased of 11.7%, and the nature frequency is increased of 3%.