The high-power solid-state laser facility puts forward stringent requirements for the additional wavefront distortion and attitude stability of the large-aperture mirror. While ensuring attitude stability, the peak-to-valley (PV) value of additional wavefront distortion caused by low-stress mounting is required to be less than λ/3 (wavelength λ=633 nm). In this paper, a mounting technology of large aperture mirror with three-point front support and eight point side fixing is proposed. The additional wavefront distortion caused by the mounting structure is simulated and experimentally studied. And the attitude stability of mirror under different working conditions is experimentally researched. The results show that the PV value of additional wavefront distortion introduced by this mounting method is about 23.6 nm, and the PV value of the mirror pointing under different conditions of vibration, shaking, and flipping is less than 50 μrad. The additional wavefront distortion and attitude stability meet the requirements of high-power lasers.