Potassium dihydrogen phosphate and its deuteride (KDP/DKDP) are the only tripled frequency crystals used for inertial confinement fusion. The photonic behavior of KDP under laser irradiation is unknown. In this study, the ultraviolet photon transport behavior of KDP with different growth environments has been simulated based on the Monte Carlo method. By comparison, it is shown that the linear absorption of filtered grown crystal is obviously weaker, and the relaxation time is much longer. Moreover, the concentration of defects inside KDP is the critical cause of linear absorption and relaxation time. Finally, the influence of multi-photon absorption on the damage of KDP is discussed.