The nonlinear optical polyimide (NLOPI) attached with azobenzene chromophore side-chain is synthesized by diazo coupling reaction of 4-nitrobenzenediazonium tetrafloroborate to poly(amic acid) in 1-methyl-2-pyrrolidone and imidization reaction at 250 ℃ for 2 h. The photoisomerization property of the NLOPI is investigated. The effects of the laser reaction time and laser power on the photoisomerization property of NLOPI film are studied. When the NLOPI film is irradiated by the 532 nm YAG laser, the absorption peak of NLOPI at 500 nm decreases with rising the laser power and extending laser reaction time, while the absorption at 360 nm increases steadily. The third-order nonlinear optical property of the nonlinear optical polyimide attached with azobenzene chromophore side-chain was studied by Z-scan technology. On the effect of 532 nm laser, the nonlinear refractive index and nonlinear absorption properties of the NLOPI are all negative, which shows that the NLOPI is self-scattering media. The nonlinear refractive index (n2), nonlinear refractive coefficient (γ), nonlinear absorption coefficient (β) and the third-order nonlinear susceptibility (χ(3)) of the NLOPI are -1.62×10-7 esu, -4.04×10-14 m2/W, 3.98×10-8 m/W and 3.41×10-18 m2/W, respectively.