Electrostatic discharge(ESD) is a common defect in TFT-LCD rubbing process, For example, the ratio of ESD is 20% at 317.5 mm(12.5 in) product, it is a great influence on the yield of products. The causes of ESD in rubbing process is studied with the theoretical analysis and experiment. Experiments show that the main reason for ESD is that there are large floating metal on the TFT substrate. In rubbing process, the charge is easy to accumulate on the TFT substrate and burning down the electric circuit, so the panel is abnormal. ESD can be reduced through controlling rubbing process and optimizing design. In process, increasing humidity and coating electrostatic prevention and controlling the life time of rubbing cloth can improve ESD. In design, by changing the large floating metal into small floating metal, ESD can be improved. By optimizing the process and design, the ESD ratio is reduced from 20% to 0%, which greatly improves the panel quality and reduced the product cost.