X-ray phase contrast imaging always provides high density resolution for weakly absorbing material, and shows wide prospect of application in many fields such as medicine, biology and material science. However, due to the limitation of interferometic imaging method, diffraction enhanced imaging method and in-line imaging method, these methods need either highly coherent or highly monochromatic X-ray, and cannot provide a large field of view, none of them is very widely used. Grating imaging overcomes the limitations of above imaging methods and enables phase contrast imaging to develop into the form of cone-beam imaging. The research of the reconstruction algorithm of cone-beam phase X-ray computer tomography (CT) is studied, based on the characteristic of cone-beam grating imaging and the theory of Feldkamp-Davis-Kress (FDK) reconstruction algorithm. This method belongs to filtered back-projection and can reconstruct the phase item of object directly with the derivative of the phase term as projection, and the algorithm is proved by simulated results.