A cone beam CT imaging system incorporates the phase contrast in-line method, in which the phase coefficient rather than only the attenuation coefficient is used to reconstruct the image. Starting from the interference formula of in-line holography, the terms in the interference formula can be approximately expressed as a line integral that is the requirement for all CBCT algorithms. So, the CBCT reconstruction algorithms, such as the FDK algorithm, can be applied for the in-line holographic projections.