Abstract: The contraction section is an important part of the high-speed wind tunnel. The surface accuracy of the contraction section has a great impact on the flow field quality of the high-speed wind tunnel. The contraction section of a special wind tunnel is made of stainless steel. Its flow channel is a large-diameter, thin-walled and high-precision curved surface at the inlet of 7 m. The wall thickness of the contraction section is thin, the ribs are sparse, the overall stiffness is weak, and the processing is easy to deform. Through process research, a process method of mutually verifying deformation by using coated blade, differentiated cutting parameters, zonal alternating normal machining, on-line monitoring and sample measurement is explored, which not only ensures the requirements of profile accuracy, but also greatly improves the work efficiency, and successfully solves the problem of high-precision surface machining of thin-walled shrinkage section of large-diameter stainless steel.