A frequency spectral coding method based on a practical CCD model was added into a photo-electronic imaging system to overcome the CCD limitation on spatial resolution and to achieve geometric superresolution imaging. The working mechanism of the geometric superresolution imaging with an optical mask was introduced. On the basis of the practical CCD model, the optical mask was placed on the Fourier transform plane of the 4f imaging system to improve the image resolution. A mathematical model of the imaging system was established and rigidly analyzed. The proposed frequency spectral coding method based on the CCD practical model was demonstrated to be validly in theory. Mathematical modeling and simulation on the proposed method in one dimensional optical mask were performed. Simulation results show that this method enable to solve the spectral aliasing caused by the separations among the pixels and the low-pass effect due to the CCD nonzero pixel size. To compare with the conventional approach, this new method is much easy to implement and has a simple structure.