A gradient index array, which has plural gradient index rods, is installed in the LED print head. In order to improve optical resolving power of the gradient index array, shielding the rays which blurred images was investigated by using the illumination analysis. In the calculation model, apertures arranged in such a position that outer portions of surfaces of rods in the gradient index array were shielded and the rays near axes of the rods were transmitted.The illumination analysis was a certain kind of the Monte Carlo calculation; a large amount of random rays was radiated from light sources to images in optical models.In this study, alterations of the dot diameter and the dot irradiance caused by radiuses of apertures change were analyzed by using the illumination analysis.The current results in the illumination analysis showed that arranging apertures in the gradient index array provided small dots. Arranging the smaller apertures caused the dots became smaller. At the same time, the reduction in the radius of the apertures increased amounts of the shielded rays so that the dot irradiance became lower.In addition, arranging the apertures and the reduction in the radius of the apertures enlarged the focus of the gradient index array.Furthermore, the reduction in the radius of the apertures provided the larger focal depth.Arranging apertures in gradient index array are effective to control the aberrations. The current analysis shows the LED print head with the apertures will expose smaller dots than a LED print head without the apertures does. In addition, arranging the apertures will permit to ease assembly accuracy of the LED print head.The apertures are effective to correct the aberrations; however, apertures cannot correct the field curvatures and the distortions. Therefore, the higher resolution images require other investigations to correct these optical problems.