Abstract: In order to study the structure control method and structure-activity relationship of multi-branched cationic polyurethane surfactants with multiple long alkyl chains, isophorone diisocyanate (IPDI), N-methyldiethanolamine, cetyl alcohol and bromine Substituted alkanes are used as raw materials to prepare a series of multi-branched long-chain alkyl quaternary ammonium polyurethane surfactants (SC2、SC3、SC4). The structure of the product was confirmed by infrared spectroscopy, gel chromatography and proton nuclear magnetic resonance spectroscopy. The critical surface tension, Krafft point, foamability, emulsification and salt resistance were tested. Due to the difference in polarity between monomers, products and solvents, cationic polyurethane surfactants (SC3) with three-branched long-chain alkyl groups cannot be obtained according to the formulation design. The product is a mixture of SC2 and SC4. The surface tension (γCMC) of the cationic polyurethane surfactant (SC2) with dihexadecyl group is 23.61mN/m, the corresponding critical micelle concentration (CMC) is 0.30×10-3mol/L, and the Krafft point is 23. ℃; The surface tension (γCMC) of the cationic polyurethane surfactant (SC4) with four hexadecyl groups is 30.35mN/m, the CMC is 0.25×10-3mol/L, and the Krafft point is 41℃; at the same time, the product It has high surface activity and good emulsification, foaming and salt tolerance. The results show that for surfactants with complex structures, the preparation method based on the reaction of isocyanate with hydroxyl is simple and reliable. Keywords: polyurethane surfactants; hyperbranched; cationic; structure-activity relationship