Well-defined amphiphilic tri-block copolymer PVP-b-PMMA-b-PVP was prepared for the first time via successive reversible addition fragmentation chain transfer (RAFT) polymerization using carboxyl-terminated trithiocarbonate as the RAFT agent. The structure of the copolymer was characterized using FTTR, GPC and 1H NMR. The block copolymer could be directly blended with polyethersulfone (PES) as a macromolecule additive using N-methyl-2-pyrrolidone (NMP) as the solvent to prepare membranes. The water contact angles for the modified membranes decreased obviously, and therefore, the protein adsorption amount on the membrane surface decreased.