Novel waterborne polyurethane (WPU) with side-chained Phenylazonaphthalene group was prepared by step-growth addition polymerization between isophorone diisocyanate (IPDI), polytetramethylene ether glycol (PTMG), 2, 2-dimethylol propionic acid (DMPA) and a self-made azo diol, N,N-(2-hydroxyethyl)-4-phenylazo naphthylamine (HPN), as a chain extender to partially substitute for 1, 4-butanediol (BDO). H-1 nuclear magnetic resonance spectra (H-1 NMR), Fourier transform infrared spectroscopy (FTIR) and Ultraviolet-Visible (UV-Vis) spectroscopy were used to research the properties of HPN and HPN-WPU. The WPU latex presented obvious trans-cis photoisomerization during UV radiation and the absorption wavelength of the HPN exhibited a blue shift after attached into polyurethane chains. It needed longer irradiated time to finish isomerization due to the emulsion aggregated states, comparing with phenylazonaphthalene monomer solution and WPU dilute solution.