This work develops a method to complete the in-flight cross calibration and verification between a radiometer and an imager hosted on aircraft. The in-flight cross calibration is data transmission through time matching, space matching, and spectral matching of two polarization instruments on the same platform, and this method can not only complete the data transfer without considering the surface type to reduce the calibration cycle but also can obtain huge and rich calibration data. The radiometer is the particulate observing scanning polarimeter (POSP), which takes multi-angle, photo-polarimetric measurements in several spectral channels. The POSP measurements in the bands of 670nm and 865nm used in this work are simultaneously measured by the simultaneous imaging polarization camera (SIPC), which is on the same aircraft. The POSP is designed to provide high precision measurements of the atmospheric or earth surface radiation polarization with a substantial along-track spatial coverage, while the SIPC can provide large spatial coverage and high-resolution measurements. Through radiometer-to-imager in-flight cross calibration, the high-precision calibration coefficient of the POSP is transmitted to the SIPC, which can effectively improve the measurement accuracy of the SIPC, and realizes the remote sensing monitoring of atmospheric fine particles with large spatial coverage and high detection precision. First, we deduce the polarization models of the POSP and the SIPC, respectively, and express them in the form of Mueller matrixes, which describe the transformation from incoming polarized radiation to measured signals. Then, we deduce the in-flight cross calibration model of the POSP and the SIPC. Finally, the in-flight experiments have been carried out to validate the radiometer-to-imager in-flight cross calibration model. The results have shown the possibility to minimize the SIPC polarization degree errors with a roughly 0.01 bias relative to POSP on the land.