KDP crystal is a nonlinear optical material that is used in inertial confinement nuclear fusion devices. However, the defects seriously reduce the optical performance such as light absorption and laser damage threshold of KDP crystals. It is thus of great significance to investigate the influence mechanism of KDP crystal defects on its electronic structure and optical properties for the improvement of its optical properties. In this paper, the structure, stability and electronic structure of hydrogen and oxygen vacancy defects (i.e., VH and VO) on the growth surfaces (100) and (101) of KDP crystals were investigated by using the first-principle calculation. The effect and microscopic mechanism of acidic environment on the structure and properties of surface defects were also discussed. The results indicate that the VH and VO defects both are easier to be formed on the surfaces (100) and (101) rather than in bulk KDP crystal. The surface (100) has an intense tolerance for surface VH and VO defects, while VO on the surface (101) prefers to lose electrons, and introduces a deep defect level in the band gap, thusdamagingthe optical properties of the KDP crystal. In addition, acidic environment canlead to more VO defects on the surface (100) and introduce the defect level in the band gap. Also, acidic environment is conducive to the repair of the VH defects on the surfaces, and can eliminate the defect states introduced by the surface VO defects on the surface (101), which is conducive to improving the quality and optical quality of the crystal surfaces.