Abstract: The damage growth threshold of fused silica optical elements under single-wavelength irradiation and dual-wavelength laser irradiation was studied based on image processing methods. Through real-time acquisition of the damage image and the spot spatial energy distribution, the energy density at the location where the damage growth occurs was obtained. Aiming at the experimental data of the damage growth of fused silica optical elements under 3\omega irradiation, 3\omega and 1\omega simultaneous irradiation, the differences between the results obtained by the image processing method and the traditional damage growth threshold R-on-1 measurement method (GB) were compared and analyzed. The results show that the image processing method used in this paper can solve the calculation error problems caused by the traditional method that the non-uniform spot with energy density distribution is equivalent to the flat top spot with uniform distribution when the damage of fused silica optical element increases under the non-uniform spot of small aperture irradiation, and reduce the effect of light spot caliber in damage (growth) threshold measurement.