In a gate-structured field emission display (FED), the insulator layer is used to keep an electrical insulation between the gate and cathode electrode. The reliability of the insulator layer is an important issue of FED fabrication, especially for large area device. In this study, the insulator layer was prepared using plasma enhanced chemical vapor deposition (PECVD) and the preparation parameters were optimized. Optimal insulator layers consisting of silicon oxide and silicon nitride stacked insulator layers were obtained and applied in a 10-inch ZnO nanowire FED device.