The invention relates to an X ray phase contrast imaging system and an X ray phase contrast imaging method. The system comprises an X ray device, a grating system, a detection unit, a data processing unit and a relative shifting device, wherein the X ray device emits X ray bundles to a detected object; the grating system comprises a first absorption grating and a second absorption grating and is positioned on a direction of an X ray, and the X ray refracted by the detected object forms a variable-intensity X ray signal through the first absorption grating and the second absorption grating; the detection unit receives the variable-intensity X ray signal and converts the variable-intensity X ray signal into an electrical signal; the data processing unit processes and extracts the refraction angle information in the electrical signal and computes pixel information by utilizing the refraction angle information; and the relative shifting device is used for enabling the detected object to relatively shift relative to the imaging system. The imaging system carries out phase contrast imaging for the detected object within a certain relative shifting range of the imaging system and the detected object at a plurality of positions so as to obtain a plurality of images of the detected object. The images are converted into the images on the same reconstruction plane so as to carry out three-dimensional image reconstruction.