The beam height of the main girder fulcrum section is one of the important design parameters of the extradosed cable-stayed bridge. In order to study the influence of the beam height of the main girder fulcrum section on the mechanical performance of the main girder of the extradosed cable-stayed bridge, the parameter sensitivity analysis was carried out. The analysis kept the cable force, the number and location of longitudinal prestress of the main girder, and the beam height of the mid-span section unchanged and only changed the beam height of the main beam fulcrum section. The influence of the change on the bending moment, stress, and stiffness of the main girder under the bridge completion state, as well as the stress, bending moment, strength, and load-strength ratio of the main girder under the normal use limit state and the bearing capacity limit state was analyzed. The results show that the stress, internal force, strength, and load-strength ratio of the main girder of the extradosed cable-stayed bridge are highly sensitive to the beam height of the main girder fulcrum section. With the increase in the main girder fulcrum section, the negative bending moment of the corresponding main girder under the bridge completion state decreases; the bending strength of the main girder increases; the compressive stress of the upper edge of the main girder increases, and the compressive stress of the lower edge decreases. The change range of the compressive stress of the lower edge is greater than that of the upper edge, and the change range is greater as it is closer to the fulcrum section. The influence range is mainly from the side span L₁/3 position (L₁ is the side span length) centered on the main pier to the middle span L₂/4 position (L₂ is the middle span length).