Abstract: Quasi-static tests were conducted on damaged timber hoop-tenon joints strengthened with dampers. Based on energy transformation and dissipation theory, hysteresis curves, skeleton curves, and energy indices, including input energy, hysteretic energy dissipation, and elastic strain energy, were analyzed before and after strengthening. Damper strengthening achieved fuller hysteresis loops and larger enclosed areas, indicating increased load capacity and energy dissipation. The total input energy, hysteretic energy dissipation, and elastic strain energy were significantly increased, with the largest increase observed in hysteretic energy dissipation. Prestressing further increased the joint energy level but had little effect on the energy distribution. The results demonstrate that the damper effectively improves the mechanical performance of damaged hoop-tenon joints and provides technical support for strengthening historic timber structures.