For the advancements of imaging fiber bundle fabrication technology with high resolution, traditional high-performance photoelectric imaging instruments become flexible with greatly reduced volume and weight. However, traditional image quality evaluation models are limited by the pixel coupling discrete sampling effect of array fiber image bundles and array CCD. On the basis of the transfer process of grayscale cosine distribution optical signal in array fiber image bundles and array CCD, a mathematical model of coupled modulation transfer function (Coupled-MTF) for coupled discrete sampling system is established. Results show that the coupled-MTF converges to a fixed value when the deviation between an input signal spatial frequency and Nyquist frequency is 1% and the total number of pixels in the array is more than 1000. A small frequency deviation corresponds to a slow convergence velocity of the coupled-MTF oscillation. The oscillation amplitude of coupled-MTF differs in tangential and sagittal directions in a manner related to the corresponding pixel coupling deviation. The coupled-MTF periodically oscillates with the coupling deviation between the array fiber image bundles and the array CCD. One cycle is equivalent to the diameter of fiber cladding. The results show that the coupled-MTF shows different characteristics from the modulation transfer function of classical space invariant imaging system.