The simultaneous imaging polarimeter can obtain the transient polarization characteristics of moving objects, and it has a wide application prospect. However, the polarization detection channels differ in spatial and radiation response, which interferes with the accurate establishment of the instrument Muller matrix. The system error source is analyzed, and the calibration and preprocessing method is proposed for the amplitude divided simultaneous imaging polarimeter. The system error of polarization imaging detection is eliminated by the calibration and correction of non-uniformity of detectors, inconsistency of radiation response, deviation of polarizers oriented angles, and difference of instantaneous field of views. The results show that after the calibration and preprocessing, the CCD non-uniformity of every channel decreases by 2.24% on average, the absolute values of radiation response differences ratio decrease by 17.22% on average, the actual polarizer oriented angles are corrected by 1.71° on average, and the imagery pixel offsets are corrected by 1.87 pixel on average. After correction, the measurement error of polarization degree and polarization angle decrease by 0.47 and 32.84°, respectively. The outdoor scene is measured and tested, the Stokes parameters are calculated correctly after preprocessing, and the physical characteristics of different materials are highlighted after the polarization imaging fusion.