<p>Milling deformation caused by initial internal stresses of parts and residual stresses induced during processing is a common issue during the machining of thin-walled parts. Although aging treatment effectively controls this problem, it faces unique challenges in thin-walled curved parts: First, curved parts feature spatial structures with unclear deformation mechanisms, differing from planar parts; second, the application stages and sequences of aging treatment for deformation control currently rely heavily on experience. To address this, this study took spherical shells as the research object to explore the application of aging treatment in controlling their machining deformation. Firstly, an improved spherical shell surface-fitting algorithm was proposed to calculate the 3D deformation field and analyze the specific deformation modes of spherical shells (typical thin-walled curved parts) during machining. Secondly, combined with optimized machining paths, experiments were designed to determine the optimal application stage and sequence of aging treatment for effective deformation control. Meanwhile, electron backscatter diffraction (EBSD) was used to analyze changes in grain size and dislocation density after aging. The results show that the sequence of heat treatment followed by cryogenic treatment is superior. Compared with untreated samples, this sequence increased grain quantity and reduced dislocation density by 28.4%. Conducting aging treatment before finishing minimized machining deformation: Maximum positive deformation decreased by 38.1%, maximum negative deformation by 12.5%, and deformation mean square error (MSE) by 6.8% compared with aging before roughing.</p>