Wafer transfer robot hand is an important component equipment to realize high precision and high efficiency automation in the process of wafer handling. The structural natural frequency directly affects the motion control performance of wafer transmission during operation. Based on the principle of planar 3-joint direct drive rotation motion and vertical lift motion, a SCARA (Selective Compliance Assembly Robot Arm) four-degree-of-freedom wafer transfer robot hand is designed. Firstly, the modal analysis of the ultra-thin mechanical finger of the SCARA wafer transfer robot hand is carried out by Ansys Workbench software. The structural size of the finger is optimized by using the uniform wheel rib structure, and the optimized first-order mode is increased by 42.79%. Then, Ansys Workbench is used to optimize the overall structure of wafer transmission. It is found that the stiffness of the base part is weak, which is the main reason for the low-order mode of the whole robot hand. For this, the structure optimization is carried out for the base, and the optimized first-order and second-order modal frequencies are increased by 52.03 % and 30.55 % respectively. Through structural optimization, the overall low-order mode of the wafer transfer robot hand is improved, and the accuracy and stability of the motion control process of the wafer transfer robot hand are improved, thereby reducing the possibility of resonance and avoiding resonance, and effectively ensuring the stability and reliability of the wafer transfer robot hand in actual work.