A potassium dihydrogen phosphate (KDP) crystal is set to be a vital factor in inertial confinement fusion (ICF). This paper focuses on how to reduce the gravitational distortion and increase the second-harmonic generation (SHG) efficiency of the KDP crystal. Multipoint support mounting configurations are proposed. Their influence on distortion and SHG efficiency is analyzed. Mechanical and optical models are established, and the distortion of the KDP crystal is calculated using the finite-element methods. In addition, phase mismatch caused by distortion and SHG efficiency is calculated and analyzed. The numerical results reveal that multipoint support is a suitable mounting configuration as it has little distortion and increases SHG efficiency. Multipoint support mounting configuration is well applied in the ICF facility.