Abstract: Polarimetric SAR technology is widely used in remote sensing and earth observation. Before any quantitative research or application are carried out, polarimetric calibration must be applied on the acquired images. The current polarimetric calibration schemes generally use distributed targets to solve crosstalk and cross-polarization channel imbalance errors. Therefore, it is necessary to extract the distributed targets that satisfy certain scattering characteristics before calibration. In this paper, we propose an automatic method of reference samples extraction for polarimetric calibration, by exploiting the polarization and distribution characteristics of helix scattering. According to the polarization target decomposition, we constructe a helix scattering ratio feature, and adaptive threshold segmentation method is also used to extract the reference samples automatically. A C-band airborne polarimetric SAR image from the Institute of Electronics, Chinese Academy of Sciences is tested. The results show that this method can maintain the correctness of polarimetric calibration, and can improve the calibration accuracy comparing with the algorithms based on polarimetric correlation coefficient or scattering power.