To determine the ultimate bearing capacity of the anchorage zone in a long-span cable-stayed bridge, a typical segment of the anchorage zone was selected for horizontal force mechanism analysis and model loading test, and its load-carrying behavior and deformation characteristics were subsequently analyzed. Results show that under the action of horizontal cable force, the bending moment is relatively large at the outer face of the end tower wall and inner face of the side tower wall, and the chamfer between the side and end walls becomes a critical section because of the combined action of tension, shear and bending. The failure mode is primarily concrete cracking: cracks appear in the end tower wall at 0.15P and penetrate the full height of the segment at 0.25P, while full-depth vertical cracks appear in the side tower wall at 0.20P. The horizontal load of the segmental mode increases nonlinearly with the deformation of the tower wall, and the ultimate bearing capacity reaches 329.70 kN, approximately 0.48P, indicating that the concrete tower wall alone cannot sustain the enormous horizontal cable force. Compared with the side tower wall, the concrete of the end tower wall is more sensitive to the horizontal cable force load. As the horizontal load increases, the load carried by the concrete is gradually transferred to the reinforcement because of the tensile cracking of the tower wall.