Aiming at the surface aberration for large-aperture and ultra-thin crystal used on the final optical system of inertial confinement fusion facility, a new design of precision mounts with low-stress, named clip-like clamped support all four edges, is proposed. Based on the harmonic conversion model and crystal alignment, the third harmonic generation efficiency will fall and the alignment focal spot will widen because of the crystal surface aberration. So the two control aims must be achieved that the surface aberration should be less than 5 μm and the crystal clamping aberration should be less than machining aberration. Based on the mechanics model, the clip-like clamped support all four edges of precise assembly structure is designed. The precision machining control, finite element analysis, and experimental verification are carried out. Experimental results show that the total surface aberration is less than 5 μm by using the method of precision mounts with low-stress, this method meets the demand of crystal surface aberration control.