The deformation of KDP crystals caused by gravity and mounting force can induce the phase mismatch, resulting in the decrease of frequency conversion efficiency. Loading strips are used to reduce the distortion in some existing methods, but it is difficult to fabricate. In order to improve the surface shapes of KDP crystals, small loading plates are used instead of loading strips. The mounting configuration is analyzed by finite element methods (FEM) and the position of the loading plates is optimized by adaptive single-objective algorithm. The results show the effectiveness of the mounting configuration in reducing the gravitational sag of KDP crystals.