In this paper, we report the damage and damage growth in potassium dihydrogen phosphate and its deuterated analog crystals. A time-resolved shadow imaging system was used to investigate the damage behavior in the bulk and on the rear surface. The damage images show differences in the damage sizes of the crystals with different deuterization rates. Theoretical simulations demonstrated that this may be due to differences in the crystallographic defects. The experimental results showed that the development of crystal damage was not only manifested as the expansion of damage on the rear surface of the crystal but also as an increase in pin-point density and size within the crystal. Crystals with higher deuterization rates had higher probability of the increasing of initial damage size, rather than the increasing of pin-point density.