Reducing protein fouling in membrane separation and purification process is still a great challenge to the widespread application of ultrafiltration (UF) membranes. In this context, polyvinylidene fluoride (PVDF) UF membranes with enhanced hydrophilicity were modified by grafting hydrophilic poly (N-acryloyl glycinamide) (PNAGA) hydrogel formed through multi-hydrogen bond self-assembly via ultraviolet (UV)-initiated radical graft polymerization. Fourier transform infrared spectra (FTIR) and X-ray photo electron spectroscopy (XPS) reveal that PNAGA gel has been grafted onto the surface of the hydrophobic PVDF membranes. Water contact angle of PNAGA modified membranes reduces from 55.2 degrees +/- 1.1 to 0 degrees within 11 s, illustrating a superior hydrophilicity. Ultrasonic 30 min and 7 days pure water filtration tests indicate that the PNAGA hydrogel layer has good stability. The results from anti-fouling test show that, when the pH is 7.0, the flux recovery rate of modified membrane maintains at 99%, the total fouling rate is as low as 30%, and the irreversible fouling rate is only 1.2%. Furthermore, the fouling mechanism investigation shows that fouling layers are not easy to form on the anti-protein-fouling PNAGA hydrogel grafted membranes. This work provides new insights for anti-fouling membrane design and application in protein purification, bio-separation and so on.