In this work, the influence factor for Electrostatic Dis-charge [ESD] on amorphous Indium Gallium Zinc Oxide Thin Film Transistors [a-IGZO TFTs] was studied using glass substrate with different properties. We identified glass back side roughness and sag have connection with ESD defect rate, the result showed higher glass substrate sag and lower back side roughness with higher ESD defect rate after process.