This study aimed to mitigate severe silica fouling and improve the removal efficiency of pharmaceutical and personal care products (PPCPs) through in-situ modification of a nanofiltration membrane (NF270) by using the concentration-polymerization-enhanced radical graft polarization method. Two modification agents were applied with different dosages-3-sulfopropyl methacrylate potassium salt and 2-hydroxyethyl methacrylate. Results show that membrane modification can effectively reduce silica fouling compared with virgin NF270, and the flux decline was fully reversible. The permeate flux of modified membranes increased with increasing monomer concentration due to the increasing degree of grafting and hydrophilicity. The increase slightly compromised the rejection of NaCl, but did not compromise that of PPCP. Instead, PPCP rejection by modified membranes before silica fouling was significantly higher than that by virgin NF270, especially for neutral carbamazepine. Moreover, membrane modification enhanced the rejection of neutral PPCPs after silica fouling by mitigating foulant deposition on the membrane surface. The fouling mechanism was confirmed to switch from gel layer formation to intermediate blocking or complete blocking. Therefore, the in-situ modification of NF270 proved to be effective for mitigating silica fouling and improving PPCP rejection.