In order to quantitatively investigate image quality improvement of area CCD subpixel imaging and influence of fill factor on image quality, a mathematical model was established to simulate subpixel imaging of array CCD with different fill factors. Without consideration of noise influence, simulation experiment for a sub-image of ISO12233 standard resolution card was performed on Matlab. Experiment results illustrate that, when fill factor is 100%, compared with common imaging mode of array CCD, gray mean gradient (GMG) of diagonal subpixel and four-point subpixel imaging mode was increased by 2.997 0, 3.413 6 respectively, and energy of Laplacian(EOL) is enhanced by 0.567 6, 0.747 8 respectively. With the same fill factor other than 100%, GMGs and EOLs of common imaging mode, diagonal subpixel imaging mode, and four-point subpixel mode are increasing in that order too. For four-point subpixel imaging mode, GMG of 69%, 44%, 25% fill factor is improved by 1.433 0, 3.337 3, 5.153 2 respectively compared with that of 100% fill factor, and EOL increased by 0.638 0, 1.704 4, 3.196 8 respectively. With the same imaging mode other than four-point subpixel, GMGs and EOLs of images obtained with CCDs whose fill factor is 100%, 69%, 44%, 25% increase too. Research shows that subpixel technique of array CCD can improve image quality, and four-point subpixel imaging mode provides more improvement on image quality than diagonal subpixel imaging mode. In the condition of signal-to-noise ratio is met, the image quality performance becomes better when fill factor decrease for the same CCD imaging mode.