Objective: To design a testing device for measuring the radial support force and bending spring back force of stent grafts and evaluate its effectiveness. Methods: A radial force and spring-back force testing device was designed to integrate with a tensile testing machine. The radial compression and bending characteristics of stent grafts for thoracic aorta applications were analyzed, and the corresponding conversion formulas were derived. A custom stent ring fixture was fabricated, and a five-wave gradient stent was sewn. Both physical experiments and finite element simulations were conducted. Radial support forces were measured by gripping 20%, 40%, and 60% of the stent’s diameter, and bending tests were performed at angles of 60°, 90°, and 180°. The stability of the testing device was analyzed through comparative tests across different compression diameters and bending angles. Results: The device demonstrated high detection precision, stability, and accuracy, with minimal deviation across multiple measurements. The mechanical behavior of the stent observed in both finite element simulations and physical experiments showed consistent results. Conclusions: The testing device developed in this study effectively measures the mechanical changes in large-diameter stent grafts, providing a new reference for testing large-diameter stents.