Sulfonated polyethersulfone (SPES) was synthesized through a feasible way by introducing sulfonic groups onto amino-substituted PES, and characterized by FT-IR, ¹H NMR and GPC. The obtained SPES could be directly blended with PES at any ratios to prepare modified membranes. Scanning electron microscope indicated that the structure of the PES membranes had an obvious change after the modification. The water contact angles of the modified PES membranes decreased from 84^° to 68^°, and the water fluxes had a dramatic increase from 162 to 1912mL/m²mmHgh when the blended amount of SPES increased from 0 to 2wt.%. The activated partial thromboplastin time and plasma recalcification time for the modified membranes increased significantly, and the blood platelet adhesion on the PES membrane was largely suppressed after the modification. All these results indicated that the hydrophilicity and the anticoagulant activity of the modified PES membranes were improved, and the modified membranes had a potential to be used in blood purification fields.