Abstract: The projection offset significantly affects the extraction accuracy and image quality in analyzer-based imaging (ABI) system. Based on the principle of the ABI system, optical models were established to study the main causes of projection offset. The effect of projection offset on the extraction of refraction-angle was studied by computer simulation. The results show that the projection offset is mainly caused by the width of the intrinsic rocking curve and the refraction-angle. The width of the intrinsic rocking curve causes the crosstalk of X-ray between adjacent pixels with the rocking of the analyzer. The rocking curve of the boundary pixel deforms, and for the virtual pixel counts appear and abnormal rocking curve forms when samples are not completely covered with the beam. Both shape and height of the rocking curve change by the projection offset caused by refraction-angle, and pixel shifting occurs with the increase of refraction angle, further affecting the correct of the extraction of refraction-angle. The width of the intrinsic rocking curve and the refraction-angle together produce projection offset and affect the extraction of refraction-angle.