Abstract: The range calibration is one of the most important links in obtaining high precision SAR images. The traditional SAR range calibration method measures the range by the POS data and the coordinates of the ground control point. It has a large dependence on the measurement accuracy of the POS system and needs to obtain the accurate position information of the ground control point. In order to reduce the requirement of slant distance calibration for POS accuracy and position control accuracy of ground control points, a calibration method based on subaperture phase is proposed. The new range calibration based on the phase of subaperture is proposed to get better calibration effect and decrease the strong dependence on POS system. In this paper, we give a model of slant calibration method based on the SAR subaperture phases. The analysis of its Cramer-Rao to test its validity and accuracy is given at the end of the article.