Abstract: In order to prepare actual optoelectronic devices using single-walled carbon nanotubes, single-walled carbon nanotube/polyimide (SWCNT/PI) film with the single-walled carbon nanotubes in mass fraction of 0.02 was prepared by means of a new gradient temperature-elevating thermal imidization method. The reflectance, transmittance, and absorbance of the film were measured with a spectrophotometer and the linear refractive index variation with wavelength of SWCNT/PI film was obtained. Simultaneously, the Sellmeyer parameters of the SWCNT/PI film were got by fitting the Sellmeyer formula. Then, the third order nonlinear optical property of the SWCNT/PI film was studied by means of z-scanning. The experiments showed that the nonlinear absorption coefficient and the nonlinear refractive coefficient of the film were -5.3×10-9cm/W and -4.1×10-13cm2/W, respectively. The results prove that SWCNT/PI film owns strong nonlinear optical property.