The new azo benzene polyurethane (CAPU) was synthesized by diazo coupling reaction with 1,4-Diaminobenzene, sodium nitrite, and R(-)-3-chloro-1,2-propanediol. The solubility was measured with several organic solvents. Some mechanical properties of CAPU, such as tensile strength and ratio of elongation at break, were investigated. The good thermal stability of the CAPU was shown by its absorption spectrum characterized by UV-Vis spectroscopy and its melting point of 113.5°C. Moreover, the refractive index of CAPU was obtained by the attenuated total reflection (ATR) method at different temperature and wavelength, by which the materials thermo-optic coefficient was calculated. It is shown that the material has a large thermo-optic coefficient and an obvious birefringence phenomena. And the dispersion coefficient was also calculated by the Sellmeyer equation. Because of thermo-optical properties mentioned above, the CAPU could be used to design and generate the thermo-optic switch and even all-optical switch.