A hyperbranched azo polyurethane was synthesized by one-step polymerization of an A type monomer diphenylmethane-4,4′-diisocyanate and a B type monomer 4-(N,N′-bis(2-hydroxyethyl))amino-2′-hydroxyethoxyl-4′-nitro-azobenzene. The azo polymer was characterized by H nuclear magnetic resonance (NMR), ultraviolet-visible (UV-Vis) spectrum and thermal analysis. The of the polymer in dimethylformamide (DMF) solution is 488 nm. The number average molecular weight (M) determined by GPC is 9,300 with a polydispersion index 1.9. The glass transition temperature () of the polymer is 131°C observed from DSC thermogram. The results show that the azo polyurethane has been successfully synthesized through this scheme. Surface-relief-gratings (SRGs) were fabricated on the polymer film after being irradiated by interference pattern of Ar laser beams for 1,000 s. The surface modulation depth and the grating space period measured by AMF are 67 and 770 nm, respectively.