The initial damage and damage growth of fused silica optical elements irradiated by 3ω alone, by two wavelengths (3ω+2ω and 3ω+1ω) at the same time were studied. When the energy density of 3ω is near its threshold, the influence of 2ω and 1ω of low energy density on the initial damage and damage growth is studied. The energy coupling mechanism between wavelengths is analyzed. The results show that: When the energy density of 2ω or 1ω is much lower than its threshold, irradiating at the same time, their effects on the initial damage probability and damage growth threshold can be ignored. But the initial damage degree and damage growth coefficient will increase. The measurement of shock wave velocity based on femtosecond dual pulse imaging shows that, when 3ω and 1ω irradiate at the same time, the energy coupling effect between wavelengths will promote the deposition efficiency of laser energy to materials.