The initial damage and damage growth of fused quartz optical elements irradiated by fundamental frequency, double frequency and triple frequency lasers alone and at the same time are studied comparatively. The effects of fundamental and double frequencies on the initial damage and damage growth induced by triple frequencies are emphatically studied. The conversion factors of fundamental frequency and double frequency relative to triple frequency are analyzed. Research results show that, when the energy density of fundamental frequency and double frequency is low, their influence on damage probability curve of triple frequency can be neglected. However, it will cause an increase in the degree of damage. In multi-wavelength simultaneous irradiation damage growth, the damage growth threshold mainly depends on the energy density of triple frequency, and the damage growth coefficient is related to the total energy density. The conversion factor can reflect both the wavelength effect of initial damage and damage growth and the energy coupling effect between wavelengths.