Through two-dimensional numerical simulations, we analyzed the effects of new cell structure for the luminous efficacy improvement in an ac plasma display panel. In the new structure with 5 electrodes, two auxiliary electrodes are arranged between X and Y electrodes with long gap. Through the application of adequate auxiliary pulse on the address electrode, the luminous efficacy in the new cell structure showed the improvement of 52[%] in comparison with that of conventional cell structure with short gap between X and Y electrodes. Consequently, as the short gap discharge between auxiliary electrodes decreases and the long gap discharge between X and Y electrodes increases, the result of VUV generation efficacy shows higher improvement. The reliability of simulation result could he confirmed by the experimental result in the test panel.