[en] The linear optical properties of potassium dihydrogen phosphate (KDP) with oxygen vacancy are investigated with first-principles density functional theory calculations. We use Heyd–Scuseria–Ernzerhof (HSE06) functional to calculate the linear optical properties because of its accuracy in the band gap calculation. Compared with the perfect KDP, we found that due to the defect states located at the band gap, the defective KDP with oxygen vacancy has new optical adsorption within the energy region from 4.8 eV to 7.0 eV (the corresponding wavelength region is from 258 nm to 177 nm). As a result, the oxygen vacancy can decrease the damage threshold of KDP crystal. It may give a direction to the KDP production for laser system. (paper)