In this paper, the concentration distribution of electrons, ions and free radicals in remote argon plasma was studied by using double suspension probe and electron spin resonance method to predict the optimal surface modification region. Then, PES membranes were placed in this region and modified by remote argon plasma. Water contact angle measurement, X-ray photoelectron spectroscopy and scanning electron microscope were used to characterize the surface structure and properties of PES membranes. Finally, the separation performance and anti-pollution performance of membranes before and after modification were analysed in bovine serum albumin separation experiment. The results showed the electron and ion concentrations in the argon plasma gradually decrease along the axial distance, close to 0 after 30cm, and the free radical concentration at 40cm still remains above 90%, which was the best possible surface modification region. In the remote region, oxygen-containing groups and nitrogen-containing groups were introduced in PES membranes surface, and the (O+N)/C atomic ratio of the membrane was increased from 0.18 to 0.46 to enhance the surface polarity of the membrane. The modified PES membranes in remote region obtained a higher hydrophilicity and the etching by electron and ions on PES membrane surface was prohibited. Under optimal processing conditions, the contact angle decreases from 67° to 18° and the membrane fouling rate after modification reduces from 70.3% to 64.7%.