The modified driving waveform is proposed to improve the characteristic of the write discharge in the open dielectric structure of the AC type plasma display panel. An open dielectric is a structure in which the sustain discharge is more easily generated by removing the dielectric layer between the electrodes of the upper plate in order to increase the luminance of the AC PDP. Though the sustain discharge easily occurs when the conventional driving method was used for the open dielectric, the characteristic of the writing discharge was relatively poor. Previous studies have suggested a method to improve the characteristics of the write discharge, but it has been disadvantageous in that an excessive reset discharge due to a high voltage causes a low contrast ratio and a high voltage was applied in the negative direction. In this study, threshold voltage (Vt) closed curves of conventional and open dielectric structures were measured and the wall voltage vector inside the cell was analyzed by the applied driving waveform. Based on these results, the modified driving waveform is proposed to improve the write discharge characteristics. Compared with the conventional driving waveform, the write discharge delay time is shortened by about 0.3 mu m in each write pulse.