Abstract: A torsion-bending composite moment loading method was developed for use in a thermal vacuum environment to simulate the thermo-mechanical and multiphysics-coupled environmental loads experienced by the rotary shaft assembly of the Chang’e lunar lander’s solar panel during in-orbit operations. The method enables the synchronous superposition of constant torque, sinusoidal alternating torque, and static bending moments. A dedicated loading device and a friction-reduction mechanism were designed to ensure loading accuracy and environmental compatibility. Ground-based thermal-vacuum tests under high/low-temperature cycling conditions demonstrated the feasibility and repeatability of the method, with the maximum torque loading error only 1.8%, and the bending moment loading error approximately 0.3%, both meeting the design criteria of less than 2% error. The results indicate that the proposed approach effectively simulates in-orbit mechanical conditions and provides a method with high engineering applicability, offering technical support for lifetime prediction, tolerance design, and failure-mechanism analysis of space rotary components.