Abstract: The surface damage characteristics in DKDP crystals under laser irradiation at 355 nm and 1064 nm were studied and compared by using a Nd: YAG laser. The damage precursors and mechanisms corresponding to each damage morphologies were analyzed. The damage results reveal that the surface damage in DKDP crystal is more complex than that in bulk damage. Under the irradiation laser corresponding to the pulse width of 10 ns and the damage probability at 0% − 50%, surface damage morphology in DKDP crystals mainly contained four typical damage morphology: crater with cavity, crater with flat bottom, surface damage crack, and surface ablation. Through the comparison and analysis of the imaging of optical microscope and scanning electron microscope, damage precursors that induced damage craters with bottom cavity and surface cracks were mainly bulk defects, which were the same as the precursors forming the internal damage points (pinpoints). The precursors that induced damage craters with flat bottom were relatively complex, which could be the surface contamination, surface cracks, machining defects, and shallow surface bulk defects. For surface ablation, it was mainly caused by surface contamination and surface absorption defects. Surface damage is still one of the important factors limiting the laser damage resistance of KDPD crystals.