In this paper， the resolution of the super second generation image intensifier and the third generation image intensifier under different illuminations are studied. The results show that the resolution of the super second generation image intensifier and the third generation image intensifier with the same gain， limit resolution， signal to noise ratio and modulation transfer function is constant when the input illumination is above 4.3×10^-3 lx， and does not change with the change of input illumination The resolution of the super second generation image intensifier is lower than that of the third generation image intensifier. The lower the input illumination， the greater the difference. The reason is that the third generation image intensifier has higher cathode sensitivity. The higher the sensitivity of the cathode， the higher the initial contrast of the photocathode， and the higher the contrast of the target image on the fluorescent screen， so the higher the resolution under low input illumination. Figure of Merit is an index to characterize the comprehensive performance of image intensifiers. However， when Figure of Merit is used to compare the comprehensive performance of image intensifiers， it can only be compared between the image intensifiers with the same photocathode， but not between the image intensifiers with different photocathode. Therefore， the Figure of Merit can not be used to compare the performance of super second generation and the third generation image intensifiers.