Effective PolSAR filters should not only inhibit speckles, but also preserve resolution of SAR image. However, it is difficult to achieve effectiveness in bother aspects if a fixed size filtering window is used. In this paper, the energy spectrum function of the total polarimetric power (Span) image is used to calculate homogeneity of targets and thus choose filtering window size adaptively. Then edge-aligned window is used and minimum mean square error (MMSE) is applied. According to experimental results, the proposed filter is effective in retaining SAR resolution while reducing speckles, which lays a sound foundation for post-processing of PolSAR data.