Hydrophilic poly((poly(ethylene glycol) methyl ether methacrylate) (P(PEGMA)) brushes were grafted from chloromethylated polyethersulfone (CMPES) hollow fiber membrane surface by surface-initiated atom transfer radical polymerization(SI-ATRP) to improve the membrane’s hydrophilic property. The CMPES hollow fiber membrane was prepared by phase inversion process. The benzyl chloride groups on the CMPES membrane surface could afford effective macroinitiators for grafting the well-defined polymer brushes. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy confirmed the grafting of P (PEGMA) chains. Field emission scanning electron microscopy (FESEM) was used to characterize the surface morphology of the CMPES membrane and modified membrane. The grafting yield of P (PEGMA) was determined by weight gain measurement. The results showed that the number-average molecular weight (Mn) of P (PEGMA) increased with the polymerization time. It was found that the grafting of P (PEGMA) brought higher pure water flux, improved water uptake ratio and better anti-protein absorption ability to CMPES membrane after modification.