The schlieren technique is a classical optical method for smooth display and measurement. Its basic principle is to use the refractive index gradient of light in the measured flow field to be measured proportional to the flow field airflow density. It has been widely used to observe the boundary layer of gas flow, combustion, Shock waves, convection inside the gas, and wind tunnels and water tunnels. In the ultra-high wind tunnel schlieren system, the surface accuracy of the main mirror has a great influence on the image quality. In order to obtain a good schlieren image, the RMS<λ/40 (λ=633nm) of the mirror after deformation is required in the design. There are many reasons for the distortion of the mirror surface, such as the temperature distribution of the external environment, the stress birefringence of the material inside, the mode of the mirror body and the stress caused by the clamping, the gravity of the body and the installation direction of the optical axis.For large-diameter mirrors, different adjustment methods will have a great influence on the stress birefringence distribution and mirror distortion of the mirror body. Reasonable adjustment structure can well guarantee the surface accuracy of the mirror surface and affect its image quality. Minimized.