Abstract: DKDP crystal was grown from 80%-deuterated solution of high pure materials and the crystal was cut to type Ⅱ tripler sample. The major problem of DKDP crystal for third harmonic generation (THG) is its low laser-induced damage thres-hold with respect to KDP, which greatly limits energy fluence of output laser and crystals’ life. Laser-induced damage thres-hold of DKDP crystal for THG was measured under different wavelengths and the effect of laser annealing was also investigated. The experiment shows that laser annealing could obviously improve laser-induced damage threshold of DKDP crystal. The thres-hold is improved to 1.4, 1.9 or 2.7 times that before annealing for fundamental, second or third harmonic, respectively. Thus laser annealing is an effective approach to enhance laser-induc