AbstractMagnetic carbon nanomaterial (MCN) was prepared by hydrothermal method using microfluidic mixing of ferric tetroxide solution precursors, which was added into casting membrane solution, and magnetic polysulfone (PSF) composite membranes were prepared by phase inversion process after introducing an external magnetic field to treat the casting membrane solution. Microscope image depicts Fe3O4 nanoparticles are uniformly loaded on carbon nanomaterials composed of graphene oxide and carbon nanotubes, and the MCN was obtained with less agglomeration, less Fe2O3 impurities, and magnetization intensity of 53.17 emu/g, which is slightly lower than that of pure Fe3O4 (68.72 emu·g−1). Microscopic cross‐sectional view of the membranes indicate the support pore structure still keep a finger‐shaped pore structure but the surface roughness of composite membrane shows an increase in Ra value compared with the pristine PSF (6.23 nm). The hydrophilicity of membranes show a marked improvement increased in contact angle (from 73.158° to 51.854°), which effect the water flux (from 638.49 to 1089.81 L·m−2·h−1) and permeability (from 1.42 to 2.57 μm2), while the effective diameter of pore in membranes increase (from 1.3385 to 1.9078 μm) through bubble pressure method, and the rejection of bovine albumin decrease slightly (from 93.03% to 90.13%), but the values all reach over 90%, which show good permeate separation performance.