Several rules are presented in the paper to evaluate quantitively the preservation performance of polarimetric information for PolSAR filters. These rules comprise the matching coefficient, the difference plot, and the mean square errors between the polarization signatures of the original PolSAR data and those of the filtered data. They are tested in terms of experimental PolSAR data to show how they can be exploited in evaluating the preservation ability of polarimetric information. Results make evident that the rules more efficient to describe the maintainability in polarimetric information for speckle filters compared to polarization signatures.