Abstract: A five-hundred-meter Aperture Spherical radio Telescope (FAST) is supported by a cable-net structure, which enables its surface to form a paraboloid in real time under active control. However, such form-changing operation would lead to about 500MPa of a fatigue stress range for the cable-net structure. This stress range is more than twice as that defined by the relative standard. Therefore, the cable-net structure is the most critical part of a FAST reflector system. Obviously, the fatigue stress will have a significant impact on the reliability of FAST during its service life. The dimensional analysis is used for studying main factor which affects the stress range of structure. Based on the finite element software ANSYS, the form-changing of cable-net structure is simulated. At last, optimal form-changing strategy is proposed for releasing the fatigue stress of cable-net structure, which would be in favor of improving the reliability of a cable-net structure.