Aiming to increase the antifouling/antibacterial property and purifying efficiency of a polyethersulfone (PES) membrane, in this study, functional polymer brush grafted carbon nanotubes (p-CNTs) were developed as multifunctional modifiers for membrane modification. Firstly, functional molecules, methyltriethylammonium chloride (MTAC) and poly(ethylene glycol) methyl ether methacrylate (EGMA), were grafted onto the CNTs via surface initiated atom transfer polymerization (SI-ATP); then p-CNT/PES composite membranes were prepared via a phase inversion technique. The modified membranes exhibited improved surface wettability owing to the introduced EGMA brushes. As revealed by protein adsorption and protein solution ultrafiltration experiments, the p-CNTs could improve the membrane antifouling properties significantly, and the bacterial culture results suggested that bacterial adhesion and survival were suppressed by the p-CNTs. Moreover, the p-CNTs enabled the membrane adsorptive activity towards phenolic molecules, which would increase the purifying efficiency of the membranes during water treatment. In general, the fabricated p-CNT/PES composite membranes integrated favorable antifouling ability, high antibacterial activity, and efficient toxin removal ability, which might satisfy diverse separation and purification needs.