Retanning fatliquor agent amphiphilic copolymer(PNMA)was synthesized from hydrophobic monomers N-octadecyl maleic amide(NSA-18) and octadecyl methacrylate(MAO), hydrophilic monomer acrylic acid (AA), with ammonium persulfate(APS) as initiator by free radical water emulsion copolymerization during which active monomer was added dropwise.The structure of PNMA was characterized by means of FT-IR and DSC. Effect of reaction conditions on properties of PNMA were investigated by single factor experiments. under optimal conditions: mole ratio of NSA-18 to MAO3:2, mole ratio of hydrophobic monomer to hydrophilic monomers 1:3.5, mass fraction of ammonium persulfate 4.5%(base on total mass of monomer), reaction temperature 88℃, dropping time of active monomer 2h, the retanning fatliquor agent showed good thickening rate,softness and `waterproofness. Light transmittance of 1% (mass fraction) PNMA aqueous emulsion obtained was 42.7%, the thickening rate was 29.6%, and static water absorption was appropriately 43.6%.