A novel free radical interfacial copolymerization was proposed and used to prepare the amphiphilic block copolymer of acrylamide (AM) with styrene (S). In this copolymerization, a synthesized new kind of initiator, namely, amphiphilic bifunctional initiator, which has not only a hydrophilic and a hydrophobic group but also two functional groups generating radicals in both ends of its molecule, was used to initiate the interfacial copolymerization. The generated amphiphilic block copolymer was characterized by infrared analysis, differential scanning calorimetry, elemental analysis, and dissolution behavior. The migration of generated copolymer from interface to water phase was discussed.