The present invention relates to an X-ray imaging system and a method for differential phase—contrast imaging of an object. To improve calibration of differential phase—contrast imaging systems and the alignment of the gratings an X-ray imaging system is provided that comprises an X-ray emitting arrangement providing at least partially coherent X-ray radiation and an X-ray detection arrangement comprising a phase-shift diffraction grating, a phase analyzer grating, and an X-ray image detector, all arranged along an optical axis. For stepping, the gratings and/or the X-ray emitting arrangement are provided with at least two actuators arranged opposite to each other with reference to the optical axis. For calibration, calibration projections are acquired without an object, wherein, the emitted X-ray radiation or one of the gratings is stepwise displaced with a calibration displacement value. For examination, measurement projections are acquired with an object, wherein the emitted X-ray radiation or one of the gratings is stepwise displaced with a measurement, a calibration projection is associated to each of the measurement projections by registering the latter with the calibration projections.