Abstract: A commercial polyacrylonitrile (PAN) was pretreated and modified to obtain the substrate HPAN, and a ground MOF material PCN-250 as filler was blended with polyethyleneimide (PEI) and spin-coated on the HPAN substrate to obtain a PCN-250/PEI-HPAN mixed matrix membrane for nanofiltration. The characterization of MOF and the prepared mixed matrix membrane showed that the ground PCN-250 had good dispersion in water, and with the increase of the amount of PCN-250 used in the membrane preparation process, the roughness of the membrane surface and the effective area increased accordingly. Since the grain surface of PCN-250 was negatively charged, the addition of PCN-250 into polymer matrix resulted in high negative charge on the membrane surface, which improved its performance in the rejection of anionic dyes. We also characterized the membrane by SEM and AFM and optimized the membrane preparation procedure. Results show that when the loading of PCN-250 was 75%, the nanofiltration performance of the PCN-250/PEI-HPAN membrane pair was the highest, with water permeability of 1 480 L/(m²·h·MPa), and a rejection of 97.3% to the dye methyl blue.