300 m-aperture illumination helps the Five-hundred-meter Aperture Spherical radio Telescope (FAST) obtain ultra-high sensitivity beyond other single-dish radio telescopes, a great advantage in achieving several important astronomical findings recently. A 315 m-aperture deformation strategy with the ratio of 0.4350 is specially proposed in the paper in that a further increase of the illumination area by 10% can be predicated for its application. The feasibility of the new strategy is verified from the point view of structural safety of the primary reflector of FAST. At first, finite element analysis on the 315 m-aperture strategy is conducted to check the maximal stress of mesh cables. Then simulations are also performed on the sliding and rotation of reflector panels to exclude the possibility of collision between neighboring panels. Finally, statistical analysis is given on fatigue cycles and fatigue stress (stress amplitude) of mesh cables based on the actual operational data of FAST in 2022 and 2023. Applying Miner linear accumulative damage criterion with the S–N fatigue life curve model of domestically produced 1860-grade low-relaxation prestressed steel strands, the authors evaluate the fatigue damage of two typical mesh cables. The fatigue damage assessment demonstrates sufficient fatigue resistance to meet FAST’s 30 yr operational requirements.