Abstract: In order to improve the water resistance and other properties of the waterborne polyurethane, polyurethane prepolymer(PPU) was synthesized in which isophorone diisocyanate (IPDI), polytetramethylene ether glycol (PTMG), 2,2-bis(hydroxymethyl) butyric acid (DMPA) and 1,4-butanediol(BDO) were as raw materials, dibutyltin dilaurate (DBTDL) was used as catalyst. And then the hydroxyl terminated dendrimer (PAMAM-OH) was as core to synthesize dendritic waterborne polyurethane（HWPU）by graft copolymerization. The optimum synthesis conditions of PPU were optimized through single-factor experiment. The reaction time was 2h, the reaction temperature was 80℃ and n (—NCO): n (—OH) was 6:1. The performance of HWPU was characterized by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and nano particle surface potential analyzer ,as well as the water resistance, the surface roughness and the mechanical properties of films were tested. The results show that the reaction is carried out as the expected route, the particle size is 43.56 nm, the crystallinity of the film is 1.59%, the water absorption of the film is 4.8% after 24 h, the tensile strength is 39.2 MPa and the elongation at break is 376.4% as well as the surface roughness of the film is reduced. Compared with the waterborne polyurethane in which there is no PAMAM-OH, the water absorption of HWPU decreases by 67.15. Its water resistance and tensile strength both are improved.