This study proposes a model that relates the carbon fiber arrangement and orientation in CFRP to the dark-field images captured by X-ray Talbot-Lau interferometer (TLI). X-ray TLI visualizes X-ray phase contrast, which is more sensitive to light elements such as carbon, than conventional X-ray absorption contrast. By using TLI, novel non-destructive inspection (NDI) technique for CFRP reinforced by distributed discontinuous carbon fibers, which precisely evaluates local orientation and distribution of fibers in large area, can be developed. The model proposed in this study forms the basis of such NDI technique. In this paper, the model is proposed first, and material parameters needed for the model are then identified from the TLI dark-field images of the multi-fiber composite (MFC) specimens. The proposed model is validated by comparing the dark-field images simulated by the model to those experimentally measured by TLI.